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  <div class="section" id="module-subprocess">
<span id="subprocess-subprocess-management"></span><h1>17.5. <a class="reference internal" href="#module-subprocess" title="subprocess: Subprocess management."><tt class="xref py py-mod docutils literal"><span class="pre">subprocess</span></tt></a> &#8212; Subprocess management<a class="headerlink" href="#module-subprocess" title="Permalink to this headline">¶</a></h1>
<p>The <a class="reference internal" href="#module-subprocess" title="subprocess: Subprocess management."><tt class="xref py py-mod docutils literal"><span class="pre">subprocess</span></tt></a> module allows you to spawn new processes, connect to their
input/output/error pipes, and obtain their return codes.  This module intends to
replace several older modules and functions:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">os</span><span class="o">.</span><span class="n">system</span>
<span class="n">os</span><span class="o">.</span><span class="n">spawn</span><span class="o">*</span>
</pre></div>
</div>
<p>Information about how the <a class="reference internal" href="#module-subprocess" title="subprocess: Subprocess management."><tt class="xref py py-mod docutils literal"><span class="pre">subprocess</span></tt></a> module can be used to replace these
modules and functions can be found in the following sections.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last"><span class="target" id="index-0"></span><a class="pep reference external" href="http://www.python.org/dev/peps/pep-0324"><strong>PEP 324</strong></a> &#8211; PEP proposing the subprocess module</p>
</div>
<div class="section" id="using-the-subprocess-module">
<h2>17.5.1. Using the <a class="reference internal" href="#module-subprocess" title="subprocess: Subprocess management."><tt class="xref py py-mod docutils literal"><span class="pre">subprocess</span></tt></a> Module<a class="headerlink" href="#using-the-subprocess-module" title="Permalink to this headline">¶</a></h2>
<p>The recommended approach to invoking subprocesses is to use the following
convenience functions for all use cases they can handle. For more advanced
use cases, the underlying <a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> interface can be used directly.</p>
<dl class="function">
<dt id="subprocess.call">
<tt class="descclassname">subprocess.</tt><tt class="descname">call</tt><big>(</big><em>args</em>, <em>*</em>, <em>stdin=None</em>, <em>stdout=None</em>, <em>stderr=None</em>, <em>shell=False</em>, <em>timeout=None</em><big>)</big><a class="headerlink" href="#subprocess.call" title="Permalink to this definition">¶</a></dt>
<dd><p>Run the command described by <em>args</em>.  Wait for command to complete, then
return the <tt class="xref py py-attr docutils literal"><span class="pre">returncode</span></tt> attribute.</p>
<p>The arguments shown above are merely the most common ones, described below
in <a class="reference internal" href="#frequently-used-arguments"><em>Frequently Used Arguments</em></a> (hence the use of keyword-only notation
in the abbreviated signature). The full function signature is largely the
same as that of the <a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> constructor - this function passes all
supplied arguments other than <em>timeout</em> directly through to that interface.</p>
<p>The <em>timeout</em> argument is passed to <a class="reference internal" href="#subprocess.Popen.wait" title="subprocess.Popen.wait"><tt class="xref py py-meth docutils literal"><span class="pre">Popen.wait()</span></tt></a>. If the timeout
expires, the child process will be killed and then waited for again.  The
<a class="reference internal" href="#subprocess.TimeoutExpired" title="subprocess.TimeoutExpired"><tt class="xref py py-exc docutils literal"><span class="pre">TimeoutExpired</span></tt></a> exception will be re-raised after the child process
has terminated.</p>
<p>Examples:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">subprocess</span><span class="o">.</span><span class="n">call</span><span class="p">([</span><span class="s">&quot;ls&quot;</span><span class="p">,</span> <span class="s">&quot;-l&quot;</span><span class="p">])</span>
<span class="go">0</span>

<span class="gp">&gt;&gt;&gt; </span><span class="n">subprocess</span><span class="o">.</span><span class="n">call</span><span class="p">(</span><span class="s">&quot;exit 1&quot;</span><span class="p">,</span> <span class="n">shell</span><span class="o">=</span><span class="k">True</span><span class="p">)</span>
<span class="go">1</span>
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Do not use <tt class="docutils literal"><span class="pre">stdout=PIPE</span></tt> or <tt class="docutils literal"><span class="pre">stderr=PIPE</span></tt> with this
function.  The child process will block if it generates enough
output to a pipe to fill up the OS pipe buffer as the pipes are
not being read from.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.3: </span><em>timeout</em> was added.</p>
</div>
</dd></dl>

<dl class="function">
<dt id="subprocess.check_call">
<tt class="descclassname">subprocess.</tt><tt class="descname">check_call</tt><big>(</big><em>args</em>, <em>*</em>, <em>stdin=None</em>, <em>stdout=None</em>, <em>stderr=None</em>, <em>shell=False</em>, <em>timeout=None</em><big>)</big><a class="headerlink" href="#subprocess.check_call" title="Permalink to this definition">¶</a></dt>
<dd><p>Run command with arguments.  Wait for command to complete. If the return
code was zero then return, otherwise raise <a class="reference internal" href="#subprocess.CalledProcessError" title="subprocess.CalledProcessError"><tt class="xref py py-exc docutils literal"><span class="pre">CalledProcessError</span></tt></a>. The
<a class="reference internal" href="#subprocess.CalledProcessError" title="subprocess.CalledProcessError"><tt class="xref py py-exc docutils literal"><span class="pre">CalledProcessError</span></tt></a> object will have the return code in the
<a class="reference internal" href="#subprocess.CalledProcessError.returncode" title="subprocess.CalledProcessError.returncode"><tt class="xref py py-attr docutils literal"><span class="pre">returncode</span></tt></a> attribute.</p>
<p>The arguments shown above are merely the most common ones, described below
in <a class="reference internal" href="#frequently-used-arguments"><em>Frequently Used Arguments</em></a> (hence the use of keyword-only notation
in the abbreviated signature). The full function signature is largely the
same as that of the <a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> constructor - this function passes all
supplied arguments other than <em>timeout</em> directly through to that interface.</p>
<p>The <em>timeout</em> argument is passed to <a class="reference internal" href="#subprocess.Popen.wait" title="subprocess.Popen.wait"><tt class="xref py py-meth docutils literal"><span class="pre">Popen.wait()</span></tt></a>. If the timeout
expires, the child process will be killed and then waited for again.  The
<a class="reference internal" href="#subprocess.TimeoutExpired" title="subprocess.TimeoutExpired"><tt class="xref py py-exc docutils literal"><span class="pre">TimeoutExpired</span></tt></a> exception will be re-raised after the child process
has terminated.</p>
<p>Examples:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">subprocess</span><span class="o">.</span><span class="n">check_call</span><span class="p">([</span><span class="s">&quot;ls&quot;</span><span class="p">,</span> <span class="s">&quot;-l&quot;</span><span class="p">])</span>
<span class="go">0</span>

<span class="gp">&gt;&gt;&gt; </span><span class="n">subprocess</span><span class="o">.</span><span class="n">check_call</span><span class="p">(</span><span class="s">&quot;exit 1&quot;</span><span class="p">,</span> <span class="n">shell</span><span class="o">=</span><span class="k">True</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
   <span class="c">...</span>
<span class="gr">subprocess.CalledProcessError</span>: <span class="n">Command &#39;exit 1&#39; returned non-zero exit status 1</span>
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Do not use <tt class="docutils literal"><span class="pre">stdout=PIPE</span></tt> or <tt class="docutils literal"><span class="pre">stderr=PIPE</span></tt> with this
function.  The child process will block if it generates enough
output to a pipe to fill up the OS pipe buffer as the pipes are
not being read from.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.3: </span><em>timeout</em> was added.</p>
</div>
</dd></dl>

<dl class="function">
<dt id="subprocess.check_output">
<tt class="descclassname">subprocess.</tt><tt class="descname">check_output</tt><big>(</big><em>args</em>, <em>*</em>, <em>input=None</em>, <em>stdin=None</em>, <em>stderr=None</em>, <em>shell=False</em>, <em>universal_newlines=False</em>, <em>timeout=None</em><big>)</big><a class="headerlink" href="#subprocess.check_output" title="Permalink to this definition">¶</a></dt>
<dd><p>Run command with arguments and return its output.</p>
<p>If the return code was non-zero it raises a <a class="reference internal" href="#subprocess.CalledProcessError" title="subprocess.CalledProcessError"><tt class="xref py py-exc docutils literal"><span class="pre">CalledProcessError</span></tt></a>. The
<a class="reference internal" href="#subprocess.CalledProcessError" title="subprocess.CalledProcessError"><tt class="xref py py-exc docutils literal"><span class="pre">CalledProcessError</span></tt></a> object will have the return code in the
<a class="reference internal" href="#subprocess.CalledProcessError.returncode" title="subprocess.CalledProcessError.returncode"><tt class="xref py py-attr docutils literal"><span class="pre">returncode</span></tt></a> attribute and any output in the
<a class="reference internal" href="#subprocess.CalledProcessError.output" title="subprocess.CalledProcessError.output"><tt class="xref py py-attr docutils literal"><span class="pre">output</span></tt></a> attribute.</p>
<p>The arguments shown above are merely the most common ones, described below
in <a class="reference internal" href="#frequently-used-arguments"><em>Frequently Used Arguments</em></a> (hence the use of keyword-only notation
in the abbreviated signature). The full function signature is largely the
same as that of the <a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> constructor - this functions passes all
supplied arguments other than <em>input</em> and <em>timeout</em> directly through to
that interface.  In addition, <em>stdout</em> is not permitted as an argument, as
it is used internally to collect the output from the subprocess.</p>
<p>The <em>timeout</em> argument is passed to <a class="reference internal" href="#subprocess.Popen.wait" title="subprocess.Popen.wait"><tt class="xref py py-meth docutils literal"><span class="pre">Popen.wait()</span></tt></a>. If the timeout
expires, the child process will be killed and then waited for again.  The
<a class="reference internal" href="#subprocess.TimeoutExpired" title="subprocess.TimeoutExpired"><tt class="xref py py-exc docutils literal"><span class="pre">TimeoutExpired</span></tt></a> exception will be re-raised after the child process
has terminated.</p>
<p>The <em>input</em> argument is passed to <a class="reference internal" href="#subprocess.Popen.communicate" title="subprocess.Popen.communicate"><tt class="xref py py-meth docutils literal"><span class="pre">Popen.communicate()</span></tt></a> and thus to the
subprocess&#8217;s stdin.  If used it must be a byte sequence, or a string if
<tt class="docutils literal"><span class="pre">universal_newlines=True</span></tt>.  When used, the internal <a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> object
is automatically created with <tt class="docutils literal"><span class="pre">stdin=PIPE</span></tt>, and the <em>stdin</em> argument may
not be used as well.</p>
<p>Examples:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">subprocess</span><span class="o">.</span><span class="n">check_output</span><span class="p">([</span><span class="s">&quot;echo&quot;</span><span class="p">,</span> <span class="s">&quot;Hello World!&quot;</span><span class="p">])</span>
<span class="go">b&#39;Hello World!\n&#39;</span>

<span class="gp">&gt;&gt;&gt; </span><span class="n">subprocess</span><span class="o">.</span><span class="n">check_output</span><span class="p">([</span><span class="s">&quot;echo&quot;</span><span class="p">,</span> <span class="s">&quot;Hello World!&quot;</span><span class="p">],</span> <span class="n">universal_newlines</span><span class="o">=</span><span class="k">True</span><span class="p">)</span>
<span class="go">&#39;Hello World!\n&#39;</span>

<span class="gp">&gt;&gt;&gt; </span><span class="n">subprocess</span><span class="o">.</span><span class="n">check_output</span><span class="p">([</span><span class="s">&quot;sed&quot;</span><span class="p">,</span> <span class="s">&quot;-e&quot;</span><span class="p">,</span> <span class="s">&quot;s/foo/bar/&quot;</span><span class="p">],</span>
<span class="gp">... </span>                        <span class="nb">input</span><span class="o">=</span><span class="n">b</span><span class="s">&quot;when in the course of fooman events</span><span class="se">\n</span><span class="s">&quot;</span><span class="p">)</span>
<span class="go">b&#39;when in the course of barman events\n&#39;</span>

<span class="gp">&gt;&gt;&gt; </span><span class="n">subprocess</span><span class="o">.</span><span class="n">check_output</span><span class="p">(</span><span class="s">&quot;exit 1&quot;</span><span class="p">,</span> <span class="n">shell</span><span class="o">=</span><span class="k">True</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
   <span class="c">...</span>
<span class="gr">subprocess.CalledProcessError</span>: <span class="n">Command &#39;exit 1&#39; returned non-zero exit status 1</span>
</pre></div>
</div>
<p>By default, this function will return the data as encoded bytes. The actual
encoding of the output data may depend on the command being invoked, so the
decoding to text will often need to be handled at the application level.</p>
<p>This behaviour may be overridden by setting <em>universal_newlines</em> to
<tt class="docutils literal"><span class="pre">True</span></tt> as described below in <a class="reference internal" href="#frequently-used-arguments"><em>Frequently Used Arguments</em></a>.</p>
<p>To also capture standard error in the result, use
<tt class="docutils literal"><span class="pre">stderr=subprocess.STDOUT</span></tt>:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">subprocess</span><span class="o">.</span><span class="n">check_output</span><span class="p">(</span>
<span class="gp">... </span>    <span class="s">&quot;ls non_existent_file; exit 0&quot;</span><span class="p">,</span>
<span class="gp">... </span>    <span class="n">stderr</span><span class="o">=</span><span class="n">subprocess</span><span class="o">.</span><span class="n">STDOUT</span><span class="p">,</span>
<span class="gp">... </span>    <span class="n">shell</span><span class="o">=</span><span class="k">True</span><span class="p">)</span>
<span class="go">&#39;ls: non_existent_file: No such file or directory\n&#39;</span>
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Do not use <tt class="docutils literal"><span class="pre">stdout=PIPE</span></tt> or <tt class="docutils literal"><span class="pre">stderr=PIPE</span></tt> with this
function.  The child process will block if it generates enough
output to a pipe to fill up the OS pipe buffer as the pipes are
not being read from.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.1.</span></p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.3: </span><em>timeout</em> was added.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.4: </span><em>input</em> was added.</p>
</div>
</dd></dl>

<dl class="data">
<dt id="subprocess.DEVNULL">
<tt class="descclassname">subprocess.</tt><tt class="descname">DEVNULL</tt><a class="headerlink" href="#subprocess.DEVNULL" title="Permalink to this definition">¶</a></dt>
<dd><p>Special value that can be used as the <em>stdin</em>, <em>stdout</em> or <em>stderr</em> argument
to <a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> and indicates that the special file <a class="reference internal" href="os.html#os.devnull" title="os.devnull"><tt class="xref py py-data docutils literal"><span class="pre">os.devnull</span></tt></a>
will be used.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.3.</span></p>
</div>
</dd></dl>

<dl class="data">
<dt id="subprocess.PIPE">
<tt class="descclassname">subprocess.</tt><tt class="descname">PIPE</tt><a class="headerlink" href="#subprocess.PIPE" title="Permalink to this definition">¶</a></dt>
<dd><p>Special value that can be used as the <em>stdin</em>, <em>stdout</em> or <em>stderr</em> argument
to <a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> and indicates that a pipe to the standard stream should be
opened.  Most useful with <a class="reference internal" href="#subprocess.Popen.communicate" title="subprocess.Popen.communicate"><tt class="xref py py-meth docutils literal"><span class="pre">Popen.communicate()</span></tt></a>.</p>
</dd></dl>

<dl class="data">
<dt id="subprocess.STDOUT">
<tt class="descclassname">subprocess.</tt><tt class="descname">STDOUT</tt><a class="headerlink" href="#subprocess.STDOUT" title="Permalink to this definition">¶</a></dt>
<dd><p>Special value that can be used as the <em>stderr</em> argument to <a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> and
indicates that standard error should go into the same handle as standard
output.</p>
</dd></dl>

<dl class="exception">
<dt id="subprocess.SubprocessError">
<em class="property">exception </em><tt class="descclassname">subprocess.</tt><tt class="descname">SubprocessError</tt><a class="headerlink" href="#subprocess.SubprocessError" title="Permalink to this definition">¶</a></dt>
<dd><p>Base class for all other exceptions from this module.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.3.</span></p>
</div>
</dd></dl>

<dl class="exception">
<dt id="subprocess.TimeoutExpired">
<em class="property">exception </em><tt class="descclassname">subprocess.</tt><tt class="descname">TimeoutExpired</tt><a class="headerlink" href="#subprocess.TimeoutExpired" title="Permalink to this definition">¶</a></dt>
<dd><p>Subclass of <a class="reference internal" href="#subprocess.SubprocessError" title="subprocess.SubprocessError"><tt class="xref py py-exc docutils literal"><span class="pre">SubprocessError</span></tt></a>, raised when a timeout expires
while waiting for a child process.</p>
<dl class="attribute">
<dt id="subprocess.TimeoutExpired.cmd">
<tt class="descname">cmd</tt><a class="headerlink" href="#subprocess.TimeoutExpired.cmd" title="Permalink to this definition">¶</a></dt>
<dd><p>Command that was used to spawn the child process.</p>
</dd></dl>

<dl class="attribute">
<dt id="subprocess.TimeoutExpired.timeout">
<tt class="descname">timeout</tt><a class="headerlink" href="#subprocess.TimeoutExpired.timeout" title="Permalink to this definition">¶</a></dt>
<dd><p>Timeout in seconds.</p>
</dd></dl>

<dl class="attribute">
<dt id="subprocess.TimeoutExpired.output">
<tt class="descname">output</tt><a class="headerlink" href="#subprocess.TimeoutExpired.output" title="Permalink to this definition">¶</a></dt>
<dd><p>Output of the child process if this exception is raised by
<a class="reference internal" href="#subprocess.check_output" title="subprocess.check_output"><tt class="xref py py-func docutils literal"><span class="pre">check_output()</span></tt></a>.  Otherwise, <tt class="docutils literal"><span class="pre">None</span></tt>.</p>
</dd></dl>

<div class="versionadded">
<p><span class="versionmodified">New in version 3.3.</span></p>
</div>
</dd></dl>

<dl class="exception">
<dt id="subprocess.CalledProcessError">
<em class="property">exception </em><tt class="descclassname">subprocess.</tt><tt class="descname">CalledProcessError</tt><a class="headerlink" href="#subprocess.CalledProcessError" title="Permalink to this definition">¶</a></dt>
<dd><p>Subclass of <a class="reference internal" href="#subprocess.SubprocessError" title="subprocess.SubprocessError"><tt class="xref py py-exc docutils literal"><span class="pre">SubprocessError</span></tt></a>, raised when a process run by
<a class="reference internal" href="#subprocess.check_call" title="subprocess.check_call"><tt class="xref py py-func docutils literal"><span class="pre">check_call()</span></tt></a> or <a class="reference internal" href="#subprocess.check_output" title="subprocess.check_output"><tt class="xref py py-func docutils literal"><span class="pre">check_output()</span></tt></a> returns a non-zero exit status.</p>
<dl class="attribute">
<dt id="subprocess.CalledProcessError.returncode">
<tt class="descname">returncode</tt><a class="headerlink" href="#subprocess.CalledProcessError.returncode" title="Permalink to this definition">¶</a></dt>
<dd><p>Exit status of the child process.</p>
</dd></dl>

<dl class="attribute">
<dt id="subprocess.CalledProcessError.cmd">
<tt class="descname">cmd</tt><a class="headerlink" href="#subprocess.CalledProcessError.cmd" title="Permalink to this definition">¶</a></dt>
<dd><p>Command that was used to spawn the child process.</p>
</dd></dl>

<dl class="attribute">
<dt id="subprocess.CalledProcessError.output">
<tt class="descname">output</tt><a class="headerlink" href="#subprocess.CalledProcessError.output" title="Permalink to this definition">¶</a></dt>
<dd><p>Output of the child process if this exception is raised by
<a class="reference internal" href="#subprocess.check_output" title="subprocess.check_output"><tt class="xref py py-func docutils literal"><span class="pre">check_output()</span></tt></a>.  Otherwise, <tt class="docutils literal"><span class="pre">None</span></tt>.</p>
</dd></dl>

</dd></dl>

<div class="section" id="frequently-used-arguments">
<span id="id1"></span><h3>17.5.1.1. Frequently Used Arguments<a class="headerlink" href="#frequently-used-arguments" title="Permalink to this headline">¶</a></h3>
<p>To support a wide variety of use cases, the <a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> constructor (and
the convenience functions) accept a large number of optional arguments. For
most typical use cases, many of these arguments can be safely left at their
default values. The arguments that are most commonly needed are:</p>
<blockquote>
<div><p><em>args</em> is required for all calls and should be a string, or a sequence of
program arguments. Providing a sequence of arguments is generally
preferred, as it allows the module to take care of any required escaping
and quoting of arguments (e.g. to permit spaces in file names). If passing
a single string, either <em>shell</em> must be <a class="reference internal" href="constants.html#True" title="True"><tt class="xref py py-const docutils literal"><span class="pre">True</span></tt></a> (see below) or else
the string must simply name the program to be executed without specifying
any arguments.</p>
<p><em>stdin</em>, <em>stdout</em> and <em>stderr</em> specify the executed program&#8217;s standard input,
standard output and standard error file handles, respectively.  Valid values
are <a class="reference internal" href="#subprocess.PIPE" title="subprocess.PIPE"><tt class="xref py py-data docutils literal"><span class="pre">PIPE</span></tt></a>, <a class="reference internal" href="#subprocess.DEVNULL" title="subprocess.DEVNULL"><tt class="xref py py-data docutils literal"><span class="pre">DEVNULL</span></tt></a>, an existing file descriptor (a positive
integer), an existing file object, and <tt class="docutils literal"><span class="pre">None</span></tt>.  <a class="reference internal" href="#subprocess.PIPE" title="subprocess.PIPE"><tt class="xref py py-data docutils literal"><span class="pre">PIPE</span></tt></a> indicates
that a new pipe to the child should be created.  <a class="reference internal" href="#subprocess.DEVNULL" title="subprocess.DEVNULL"><tt class="xref py py-data docutils literal"><span class="pre">DEVNULL</span></tt></a> indicates
that the special file <a class="reference internal" href="os.html#os.devnull" title="os.devnull"><tt class="xref py py-data docutils literal"><span class="pre">os.devnull</span></tt></a> will be used.  With the default
settings of <tt class="docutils literal"><span class="pre">None</span></tt>, no redirection will occur; the child&#8217;s file handles
will be inherited from the parent.  Additionally, <em>stderr</em> can be
<a class="reference internal" href="#subprocess.STDOUT" title="subprocess.STDOUT"><tt class="xref py py-data docutils literal"><span class="pre">STDOUT</span></tt></a>, which indicates that the stderr data from the child
process should be captured into the same file handle as for <em>stdout</em>.</p>
<p id="index-1">If <em>universal_newlines</em> is <tt class="docutils literal"><span class="pre">False</span></tt> the file objects <em>stdin</em>, <em>stdout</em> and
<em>stderr</em> will be opened as binary streams, and no line ending conversion is
done.</p>
<p>If <em>universal_newlines</em> is <tt class="docutils literal"><span class="pre">True</span></tt>, these file objects
will be opened as text streams in <a class="reference internal" href="../glossary.html#term-universal-newlines"><em class="xref std std-term">universal newlines</em></a> mode
using the encoding returned by <a class="reference internal" href="locale.html#locale.getpreferredencoding" title="locale.getpreferredencoding"><tt class="xref py py-func docutils literal"><span class="pre">locale.getpreferredencoding(False)</span></tt></a>.  For <em>stdin</em>, line ending characters
<tt class="docutils literal"><span class="pre">'\n'</span></tt> in the input will be converted to the default line separator
<a class="reference internal" href="os.html#os.linesep" title="os.linesep"><tt class="xref py py-data docutils literal"><span class="pre">os.linesep</span></tt></a>.  For <em>stdout</em> and <em>stderr</em>, all line endings in the
output will be converted to <tt class="docutils literal"><span class="pre">'\n'</span></tt>.  For more information see the
documentation of the <a class="reference internal" href="io.html#io.TextIOWrapper" title="io.TextIOWrapper"><tt class="xref py py-class docutils literal"><span class="pre">io.TextIOWrapper</span></tt></a> class when the <em>newline</em>
argument to its constructor is <tt class="docutils literal"><span class="pre">None</span></tt>.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The newlines attribute of the file objects <a class="reference internal" href="#subprocess.Popen.stdin" title="subprocess.Popen.stdin"><tt class="xref py py-attr docutils literal"><span class="pre">Popen.stdin</span></tt></a>,
<a class="reference internal" href="#subprocess.Popen.stdout" title="subprocess.Popen.stdout"><tt class="xref py py-attr docutils literal"><span class="pre">Popen.stdout</span></tt></a> and <a class="reference internal" href="#subprocess.Popen.stderr" title="subprocess.Popen.stderr"><tt class="xref py py-attr docutils literal"><span class="pre">Popen.stderr</span></tt></a> are not updated by
the <a class="reference internal" href="#subprocess.Popen.communicate" title="subprocess.Popen.communicate"><tt class="xref py py-meth docutils literal"><span class="pre">Popen.communicate()</span></tt></a> method.</p>
</div>
<p>If <em>shell</em> is <tt class="docutils literal"><span class="pre">True</span></tt>, the specified command will be executed through
the shell.  This can be useful if you are using Python primarily for the
enhanced control flow it offers over most system shells and still want
convenient access to other shell features such as shell pipes, filename
wildcards, environment variable expansion, and expansion of <tt class="docutils literal"><span class="pre">~</span></tt> to a
user&#8217;s home directory.  However, note that Python itself offers
implementations of many shell-like features (in particular, <a class="reference internal" href="glob.html#module-glob" title="glob: Unix shell style pathname pattern expansion."><tt class="xref py py-mod docutils literal"><span class="pre">glob</span></tt></a>,
<a class="reference internal" href="fnmatch.html#module-fnmatch" title="fnmatch: Unix shell style filename pattern matching."><tt class="xref py py-mod docutils literal"><span class="pre">fnmatch</span></tt></a>, <a class="reference internal" href="os.html#os.walk" title="os.walk"><tt class="xref py py-func docutils literal"><span class="pre">os.walk()</span></tt></a>, <a class="reference internal" href="os.path.html#os.path.expandvars" title="os.path.expandvars"><tt class="xref py py-func docutils literal"><span class="pre">os.path.expandvars()</span></tt></a>,
<a class="reference internal" href="os.path.html#os.path.expanduser" title="os.path.expanduser"><tt class="xref py py-func docutils literal"><span class="pre">os.path.expanduser()</span></tt></a>, and <a class="reference internal" href="shutil.html#module-shutil" title="shutil: High-level file operations, including copying."><tt class="xref py py-mod docutils literal"><span class="pre">shutil</span></tt></a>).</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.3: </span>When <em>universal_newlines</em> is <tt class="docutils literal"><span class="pre">True</span></tt>, the class uses the encoding
<a class="reference internal" href="locale.html#locale.getpreferredencoding" title="locale.getpreferredencoding"><tt class="xref py py-func docutils literal"><span class="pre">locale.getpreferredencoding(False)</span></tt></a>
instead of <tt class="docutils literal"><span class="pre">locale.getpreferredencoding()</span></tt>.  See the
<a class="reference internal" href="io.html#io.TextIOWrapper" title="io.TextIOWrapper"><tt class="xref py py-class docutils literal"><span class="pre">io.TextIOWrapper</span></tt></a> class for more information on this change.</p>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Read the <a class="reference internal" href="#security-considerations">Security Considerations</a> section before using <tt class="docutils literal"><span class="pre">shell=True</span></tt>.</p>
</div>
</div></blockquote>
<p>These options, along with all of the other options, are described in more
detail in the <a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> constructor documentation.</p>
</div>
<div class="section" id="popen-constructor">
<h3>17.5.1.2. Popen Constructor<a class="headerlink" href="#popen-constructor" title="Permalink to this headline">¶</a></h3>
<p>The underlying process creation and management in this module is handled by
the <a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> class. It offers a lot of flexibility so that developers
are able to handle the less common cases not covered by the convenience
functions.</p>
<dl class="class">
<dt id="subprocess.Popen">
<em class="property">class </em><tt class="descclassname">subprocess.</tt><tt class="descname">Popen</tt><big>(</big><em>args</em>, <em>bufsize=-1</em>, <em>executable=None</em>, <em>stdin=None</em>, <em>stdout=None</em>, <em>stderr=None</em>, <em>preexec_fn=None</em>, <em>close_fds=True</em>, <em>shell=False</em>, <em>cwd=None</em>, <em>env=None</em>, <em>universal_newlines=False</em>, <em>startupinfo=None</em>, <em>creationflags=0</em>, <em>restore_signals=True</em>, <em>start_new_session=False</em>, <em>pass_fds=()</em><big>)</big><a class="headerlink" href="#subprocess.Popen" title="Permalink to this definition">¶</a></dt>
<dd><p>Execute a child program in a new process.  On POSIX, the class uses
<a class="reference internal" href="os.html#os.execvp" title="os.execvp"><tt class="xref py py-meth docutils literal"><span class="pre">os.execvp()</span></tt></a>-like behavior to execute the child program.  On Windows,
the class uses the Windows <tt class="docutils literal"><span class="pre">CreateProcess()</span></tt> function.  The arguments to
<a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> are as follows.</p>
<p><em>args</em> should be a sequence of program arguments or else a single string.
By default, the program to execute is the first item in <em>args</em> if <em>args</em> is
a sequence.  If <em>args</em> is a string, the interpretation is
platform-dependent and described below.  See the <em>shell</em> and <em>executable</em>
arguments for additional differences from the default behavior.  Unless
otherwise stated, it is recommended to pass <em>args</em> as a sequence.</p>
<p>On POSIX, if <em>args</em> is a string, the string is interpreted as the name or
path of the program to execute.  However, this can only be done if not
passing arguments to the program.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p><a class="reference internal" href="shlex.html#shlex.split" title="shlex.split"><tt class="xref py py-meth docutils literal"><span class="pre">shlex.split()</span></tt></a> can be useful when determining the correct
tokenization for <em>args</em>, especially in complex cases:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="gp">&gt;&gt;&gt; </span><span class="kn">import</span> <span class="nn">shlex</span><span class="o">,</span> <span class="nn">subprocess</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">command_line</span> <span class="o">=</span> <span class="nb">input</span><span class="p">()</span>
<span class="go">/bin/vikings -input eggs.txt -output &quot;spam spam.txt&quot; -cmd &quot;echo &#39;$MONEY&#39;&quot;</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">args</span> <span class="o">=</span> <span class="n">shlex</span><span class="o">.</span><span class="n">split</span><span class="p">(</span><span class="n">command_line</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="nb">print</span><span class="p">(</span><span class="n">args</span><span class="p">)</span>
<span class="go">[&#39;/bin/vikings&#39;, &#39;-input&#39;, &#39;eggs.txt&#39;, &#39;-output&#39;, &#39;spam spam.txt&#39;, &#39;-cmd&#39;, &quot;echo &#39;$MONEY&#39;&quot;]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">p</span> <span class="o">=</span> <span class="n">subprocess</span><span class="o">.</span><span class="n">Popen</span><span class="p">(</span><span class="n">args</span><span class="p">)</span> <span class="c"># Success!</span>
</pre></div>
</div>
<p class="last">Note in particular that options (such as <em>-input</em>) and arguments (such
as <em>eggs.txt</em>) that are separated by whitespace in the shell go in separate
list elements, while arguments that need quoting or backslash escaping when
used in the shell (such as filenames containing spaces or the <em>echo</em> command
shown above) are single list elements.</p>
</div>
<p>On Windows, if <em>args</em> is a sequence, it will be converted to a string in a
manner described in <a class="reference internal" href="#converting-argument-sequence"><em>Converting an argument sequence to a string on Windows</em></a>.  This is because
the underlying <tt class="docutils literal"><span class="pre">CreateProcess()</span></tt> operates on strings.</p>
<p>The <em>shell</em> argument (which defaults to <em>False</em>) specifies whether to use
the shell as the program to execute.  If <em>shell</em> is <em>True</em>, it is
recommended to pass <em>args</em> as a string rather than as a sequence.</p>
<p>On POSIX with <tt class="docutils literal"><span class="pre">shell=True</span></tt>, the shell defaults to <tt class="file docutils literal"><span class="pre">/bin/sh</span></tt>.  If
<em>args</em> is a string, the string specifies the command
to execute through the shell.  This means that the string must be
formatted exactly as it would be when typed at the shell prompt.  This
includes, for example, quoting or backslash escaping filenames with spaces in
them.  If <em>args</em> is a sequence, the first item specifies the command string, and
any additional items will be treated as additional arguments to the shell
itself.  That is to say, <a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> does the equivalent of:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">Popen</span><span class="p">([</span><span class="s">&#39;/bin/sh&#39;</span><span class="p">,</span> <span class="s">&#39;-c&#39;</span><span class="p">,</span> <span class="n">args</span><span class="p">[</span><span class="mi">0</span><span class="p">],</span> <span class="n">args</span><span class="p">[</span><span class="mi">1</span><span class="p">],</span> <span class="o">...</span><span class="p">])</span>
</pre></div>
</div>
<p>On Windows with <tt class="docutils literal"><span class="pre">shell=True</span></tt>, the <span class="target" id="index-2"></span><tt class="xref std std-envvar docutils literal"><span class="pre">COMSPEC</span></tt> environment variable
specifies the default shell.  The only time you need to specify
<tt class="docutils literal"><span class="pre">shell=True</span></tt> on Windows is when the command you wish to execute is built
into the shell (e.g. <strong class="command">dir</strong> or <strong class="command">copy</strong>).  You do not need
<tt class="docutils literal"><span class="pre">shell=True</span></tt> to run a batch file or console-based executable.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">Read the <a class="reference internal" href="#security-considerations">Security Considerations</a> section before using <tt class="docutils literal"><span class="pre">shell=True</span></tt>.</p>
</div>
<p><em>bufsize</em> will be supplied as the corresponding argument to the
<a class="reference internal" href="functions.html#open" title="open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a> function when creating the stdin/stdout/stderr pipe
file objects:</p>
<ul class="simple">
<li><tt class="xref py py-const docutils literal"><span class="pre">0</span></tt> means unbuffered (read and write are one
system call and can return short)</li>
<li><tt class="xref py py-const docutils literal"><span class="pre">1</span></tt> means line buffered
(only usable if <tt class="docutils literal"><span class="pre">universal_newlines=True</span></tt> i.e., in a text mode)</li>
<li>any other positive value means use a buffer of approximately that
size</li>
<li>negative bufsize (the default) means the system default of
io.DEFAULT_BUFFER_SIZE will be used.</li>
</ul>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.3.1: </span><em>bufsize</em> now defaults to -1 to enable buffering by default to match the
behavior that most code expects.  In versions prior to Python 3.2.4 and
3.3.1 it incorrectly defaulted to <tt class="xref py py-const docutils literal"><span class="pre">0</span></tt> which was unbuffered
and allowed short reads.  This was unintentional and did not match the
behavior of Python 2 as most code expected.</p>
</div>
<p>The <em>executable</em> argument specifies a replacement program to execute.   It
is very seldom needed.  When <tt class="docutils literal"><span class="pre">shell=False</span></tt>, <em>executable</em> replaces the
program to execute specified by <em>args</em>.  However, the original <em>args</em> is
still passed to the program.  Most programs treat the program specified
by <em>args</em> as the command name, which can then be different from the program
actually executed.  On POSIX, the <em>args</em> name
becomes the display name for the executable in utilities such as
<strong class="program">ps</strong>.  If <tt class="docutils literal"><span class="pre">shell=True</span></tt>, on POSIX the <em>executable</em> argument
specifies a replacement shell for the default <tt class="file docutils literal"><span class="pre">/bin/sh</span></tt>.</p>
<p><em>stdin</em>, <em>stdout</em> and <em>stderr</em> specify the executed program&#8217;s standard input,
standard output and standard error file handles, respectively.  Valid values
are <a class="reference internal" href="#subprocess.PIPE" title="subprocess.PIPE"><tt class="xref py py-data docutils literal"><span class="pre">PIPE</span></tt></a>, <a class="reference internal" href="#subprocess.DEVNULL" title="subprocess.DEVNULL"><tt class="xref py py-data docutils literal"><span class="pre">DEVNULL</span></tt></a>, an existing file descriptor (a positive
integer), an existing <a class="reference internal" href="../glossary.html#term-file-object"><em class="xref std std-term">file object</em></a>, and <tt class="docutils literal"><span class="pre">None</span></tt>.  <a class="reference internal" href="#subprocess.PIPE" title="subprocess.PIPE"><tt class="xref py py-data docutils literal"><span class="pre">PIPE</span></tt></a>
indicates that a new pipe to the child should be created.  <a class="reference internal" href="#subprocess.DEVNULL" title="subprocess.DEVNULL"><tt class="xref py py-data docutils literal"><span class="pre">DEVNULL</span></tt></a>
indicates that the special file <a class="reference internal" href="os.html#os.devnull" title="os.devnull"><tt class="xref py py-data docutils literal"><span class="pre">os.devnull</span></tt></a> will be used. With the
default settings of <tt class="docutils literal"><span class="pre">None</span></tt>, no redirection will occur; the child&#8217;s file
handles will be inherited from the parent.  Additionally, <em>stderr</em> can be
<a class="reference internal" href="#subprocess.STDOUT" title="subprocess.STDOUT"><tt class="xref py py-data docutils literal"><span class="pre">STDOUT</span></tt></a>, which indicates that the stderr data from the applications
should be captured into the same file handle as for stdout.</p>
<p>If <em>preexec_fn</em> is set to a callable object, this object will be called in the
child process just before the child is executed.
(POSIX only)</p>
<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p class="last">The <em>preexec_fn</em> parameter is not safe to use in the presence of threads
in your application.  The child process could deadlock before exec is
called.
If you must use it, keep it trivial!  Minimize the number of libraries
you call into.</p>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">If you need to modify the environment for the child use the <em>env</em>
parameter rather than doing it in a <em>preexec_fn</em>.
The <em>start_new_session</em> parameter can take the place of a previously
common use of <em>preexec_fn</em> to call os.setsid() in the child.</p>
</div>
<p>If <em>close_fds</em> is true, all file descriptors except <tt class="xref py py-const docutils literal"><span class="pre">0</span></tt>, <tt class="xref py py-const docutils literal"><span class="pre">1</span></tt> and
<tt class="xref py py-const docutils literal"><span class="pre">2</span></tt> will be closed before the child process is executed. (POSIX only).
The default varies by platform:  Always true on POSIX.  On Windows it is
true when <em>stdin</em>/<em>stdout</em>/<em>stderr</em> are <a class="reference internal" href="constants.html#None" title="None"><tt class="xref py py-const docutils literal"><span class="pre">None</span></tt></a>, false otherwise.
On Windows, if <em>close_fds</em> is true then no handles will be inherited by the
child process.  Note that on Windows, you cannot set <em>close_fds</em> to true and
also redirect the standard handles by setting <em>stdin</em>, <em>stdout</em> or <em>stderr</em>.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.2: </span>The default for <em>close_fds</em> was changed from <a class="reference internal" href="constants.html#False" title="False"><tt class="xref py py-const docutils literal"><span class="pre">False</span></tt></a> to
what is described above.</p>
</div>
<p><em>pass_fds</em> is an optional sequence of file descriptors to keep open
between the parent and child.  Providing any <em>pass_fds</em> forces
<em>close_fds</em> to be <a class="reference internal" href="constants.html#True" title="True"><tt class="xref py py-const docutils literal"><span class="pre">True</span></tt></a>.  (POSIX only)</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.2: </span>The <em>pass_fds</em> parameter was added.</p>
</div>
<p>If <em>cwd</em> is not <tt class="docutils literal"><span class="pre">None</span></tt>, the function changes the working directory to
<em>cwd</em> before executing the child.  In particular, the function looks for
<em>executable</em> (or for the first item in <em>args</em>) relative to <em>cwd</em> if the
executable path is a relative path.</p>
<p>If <em>restore_signals</em> is true (the default) all signals that Python has set to
SIG_IGN are restored to SIG_DFL in the child process before the exec.
Currently this includes the SIGPIPE, SIGXFZ and SIGXFSZ signals.
(POSIX only)</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.2: </span><em>restore_signals</em> was added.</p>
</div>
<p>If <em>start_new_session</em> is true the setsid() system call will be made in the
child process prior to the execution of the subprocess.  (POSIX only)</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.2: </span><em>start_new_session</em> was added.</p>
</div>
<p>If <em>env</em> is not <tt class="docutils literal"><span class="pre">None</span></tt>, it must be a mapping that defines the environment
variables for the new process; these are used instead of the default
behavior of inheriting the current process&#8217; environment.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">If specified, <em>env</em> must provide any variables required for the program to
execute.  On Windows, in order to run a <a class="reference external" href="http://en.wikipedia.org/wiki/Side-by-Side_Assembly">side-by-side assembly</a> the
specified <em>env</em> <strong>must</strong> include a valid <span class="target" id="index-3"></span><tt class="xref std std-envvar docutils literal"><span class="pre">SystemRoot</span></tt>.</p>
</div>
<p>If <em>universal_newlines</em> is <tt class="docutils literal"><span class="pre">True</span></tt>, the file objects <em>stdin</em>, <em>stdout</em>
and <em>stderr</em> are opened as text streams in universal newlines mode, as
described above in <a class="reference internal" href="#frequently-used-arguments"><em>Frequently Used Arguments</em></a>, otherwise they are
opened as binary streams.</p>
<p>If given, <em>startupinfo</em> will be a <a class="reference internal" href="#subprocess.STARTUPINFO" title="subprocess.STARTUPINFO"><tt class="xref py py-class docutils literal"><span class="pre">STARTUPINFO</span></tt></a> object, which is
passed to the underlying <tt class="docutils literal"><span class="pre">CreateProcess</span></tt> function.
<em>creationflags</em>, if given, can be <a class="reference internal" href="#subprocess.CREATE_NEW_CONSOLE" title="subprocess.CREATE_NEW_CONSOLE"><tt class="xref py py-data docutils literal"><span class="pre">CREATE_NEW_CONSOLE</span></tt></a> or
<a class="reference internal" href="#subprocess.CREATE_NEW_PROCESS_GROUP" title="subprocess.CREATE_NEW_PROCESS_GROUP"><tt class="xref py py-data docutils literal"><span class="pre">CREATE_NEW_PROCESS_GROUP</span></tt></a>. (Windows only)</p>
<p>Popen objects are supported as context managers via the <a class="reference internal" href="../reference/compound_stmts.html#with"><tt class="xref std std-keyword docutils literal"><span class="pre">with</span></tt></a> statement:
on exit, standard file descriptors are closed, and the process is waited for.</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="k">with</span> <span class="n">Popen</span><span class="p">([</span><span class="s">&quot;ifconfig&quot;</span><span class="p">],</span> <span class="n">stdout</span><span class="o">=</span><span class="n">PIPE</span><span class="p">)</span> <span class="k">as</span> <span class="n">proc</span><span class="p">:</span>
    <span class="n">log</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">proc</span><span class="o">.</span><span class="n">stdout</span><span class="o">.</span><span class="n">read</span><span class="p">())</span>
</pre></div>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.2: </span>Added context manager support.</p>
</div>
</dd></dl>

</div>
<div class="section" id="exceptions">
<h3>17.5.1.3. Exceptions<a class="headerlink" href="#exceptions" title="Permalink to this headline">¶</a></h3>
<p>Exceptions raised in the child process, before the new program has started to
execute, will be re-raised in the parent.  Additionally, the exception object
will have one extra attribute called <tt class="xref py py-attr docutils literal"><span class="pre">child_traceback</span></tt>, which is a string
containing traceback information from the child&#8217;s point of view.</p>
<p>The most common exception raised is <a class="reference internal" href="exceptions.html#OSError" title="OSError"><tt class="xref py py-exc docutils literal"><span class="pre">OSError</span></tt></a>.  This occurs, for example,
when trying to execute a non-existent file.  Applications should prepare for
<a class="reference internal" href="exceptions.html#OSError" title="OSError"><tt class="xref py py-exc docutils literal"><span class="pre">OSError</span></tt></a> exceptions.</p>
<p>A <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><tt class="xref py py-exc docutils literal"><span class="pre">ValueError</span></tt></a> will be raised if <a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> is called with invalid
arguments.</p>
<p><a class="reference internal" href="#subprocess.check_call" title="subprocess.check_call"><tt class="xref py py-func docutils literal"><span class="pre">check_call()</span></tt></a> and <a class="reference internal" href="#subprocess.check_output" title="subprocess.check_output"><tt class="xref py py-func docutils literal"><span class="pre">check_output()</span></tt></a> will raise
<a class="reference internal" href="#subprocess.CalledProcessError" title="subprocess.CalledProcessError"><tt class="xref py py-exc docutils literal"><span class="pre">CalledProcessError</span></tt></a> if the called process returns a non-zero return
code.</p>
<p>All of the functions and methods that accept a <em>timeout</em> parameter, such as
<a class="reference internal" href="#subprocess.call" title="subprocess.call"><tt class="xref py py-func docutils literal"><span class="pre">call()</span></tt></a> and <a class="reference internal" href="#subprocess.Popen.communicate" title="subprocess.Popen.communicate"><tt class="xref py py-meth docutils literal"><span class="pre">Popen.communicate()</span></tt></a> will raise <a class="reference internal" href="#subprocess.TimeoutExpired" title="subprocess.TimeoutExpired"><tt class="xref py py-exc docutils literal"><span class="pre">TimeoutExpired</span></tt></a> if
the timeout expires before the process exits.</p>
<p>Exceptions defined in this module all inherit from <a class="reference internal" href="#subprocess.SubprocessError" title="subprocess.SubprocessError"><tt class="xref py py-exc docutils literal"><span class="pre">SubprocessError</span></tt></a>.</p>
<blockquote>
<div><div class="versionadded">
<p><span class="versionmodified">New in version 3.3: </span>The <a class="reference internal" href="#subprocess.SubprocessError" title="subprocess.SubprocessError"><tt class="xref py py-exc docutils literal"><span class="pre">SubprocessError</span></tt></a> base class was added.</p>
</div>
</div></blockquote>
</div>
</div>
<div class="section" id="security-considerations">
<h2>17.5.2. Security Considerations<a class="headerlink" href="#security-considerations" title="Permalink to this headline">¶</a></h2>
<p>Unlike some other popen functions, this implementation will never
implicitly call a system shell.  This means that all characters,
including shell metacharacters, can safely be passed to child processes.
If the shell is invoked explicitly, via <tt class="docutils literal"><span class="pre">shell=True</span></tt>, it is the application&#8217;s
responsibility to ensure that all whitespace and metacharacters are
quoted appropriately to avoid
<a class="reference external" href="http://en.wikipedia.org/wiki/Shell_injection#Shell_injection">shell injection</a>
vulnerabilities.</p>
<p>When using <tt class="docutils literal"><span class="pre">shell=True</span></tt>, the <a class="reference internal" href="shlex.html#shlex.quote" title="shlex.quote"><tt class="xref py py-func docutils literal"><span class="pre">shlex.quote()</span></tt></a> function can be
used to properly escape whitespace and shell metacharacters in strings
that are going to be used to construct shell commands.</p>
</div>
<div class="section" id="popen-objects">
<h2>17.5.3. Popen Objects<a class="headerlink" href="#popen-objects" title="Permalink to this headline">¶</a></h2>
<p>Instances of the <a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> class have the following methods:</p>
<dl class="method">
<dt id="subprocess.Popen.poll">
<tt class="descclassname">Popen.</tt><tt class="descname">poll</tt><big>(</big><big>)</big><a class="headerlink" href="#subprocess.Popen.poll" title="Permalink to this definition">¶</a></dt>
<dd><p>Check if child process has terminated.  Set and return
<a class="reference internal" href="#subprocess.Popen.returncode" title="subprocess.Popen.returncode"><tt class="xref py py-attr docutils literal"><span class="pre">returncode</span></tt></a> attribute.</p>
</dd></dl>

<dl class="method">
<dt id="subprocess.Popen.wait">
<tt class="descclassname">Popen.</tt><tt class="descname">wait</tt><big>(</big><em>timeout=None</em><big>)</big><a class="headerlink" href="#subprocess.Popen.wait" title="Permalink to this definition">¶</a></dt>
<dd><p>Wait for child process to terminate.  Set and return
<a class="reference internal" href="#subprocess.Popen.returncode" title="subprocess.Popen.returncode"><tt class="xref py py-attr docutils literal"><span class="pre">returncode</span></tt></a> attribute.</p>
<p>If the process does not terminate after <em>timeout</em> seconds, raise a
<a class="reference internal" href="#subprocess.TimeoutExpired" title="subprocess.TimeoutExpired"><tt class="xref py py-exc docutils literal"><span class="pre">TimeoutExpired</span></tt></a> exception.  It is safe to catch this exception and
retry the wait.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">This will deadlock when using <tt class="docutils literal"><span class="pre">stdout=PIPE</span></tt> or <tt class="docutils literal"><span class="pre">stderr=PIPE</span></tt>
and the child process generates enough output to a pipe such that
it blocks waiting for the OS pipe buffer to accept more data.
Use <a class="reference internal" href="#subprocess.Popen.communicate" title="subprocess.Popen.communicate"><tt class="xref py py-meth docutils literal"><span class="pre">Popen.communicate()</span></tt></a> when using pipes to avoid that.</p>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The function is implemented using a busy loop (non-blocking call and
short sleeps). Use the <a class="reference internal" href="asyncio.html#module-asyncio" title="asyncio: Asynchronous I/O, event loop, coroutines and tasks."><tt class="xref py py-mod docutils literal"><span class="pre">asyncio</span></tt></a> module for an asynchronous wait:
see <a class="reference internal" href="asyncio-subprocess.html#asyncio.create_subprocess_exec" title="asyncio.create_subprocess_exec"><tt class="xref py py-class docutils literal"><span class="pre">asyncio.create_subprocess_exec</span></tt></a>.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.3: </span><em>timeout</em> was added.</p>
</div>
<div class="deprecated">
<p><span class="versionmodified">Deprecated since version 3.4: </span>Do not use the <em>endtime</em> parameter.  It is was unintentionally
exposed in 3.3 but was left undocumented as it was intended to be
private for internal use.  Use <em>timeout</em> instead.</p>
</div>
</dd></dl>

<dl class="method">
<dt id="subprocess.Popen.communicate">
<tt class="descclassname">Popen.</tt><tt class="descname">communicate</tt><big>(</big><em>input=None</em>, <em>timeout=None</em><big>)</big><a class="headerlink" href="#subprocess.Popen.communicate" title="Permalink to this definition">¶</a></dt>
<dd><p>Interact with process: Send data to stdin.  Read data from stdout and stderr,
until end-of-file is reached.  Wait for process to terminate.  The optional
<em>input</em> argument should be data to be sent to the child process, or
<tt class="docutils literal"><span class="pre">None</span></tt>, if no data should be sent to the child.  The type of <em>input</em>
must be bytes or, if <em>universal_newlines</em> was <tt class="docutils literal"><span class="pre">True</span></tt>, a string.</p>
<p><a class="reference internal" href="#subprocess.Popen.communicate" title="subprocess.Popen.communicate"><tt class="xref py py-meth docutils literal"><span class="pre">communicate()</span></tt></a> returns a tuple <tt class="docutils literal"><span class="pre">(stdout_data,</span> <span class="pre">stderr_data)</span></tt>.</p>
<p>Note that if you want to send data to the process&#8217;s stdin, you need to create
the Popen object with <tt class="docutils literal"><span class="pre">stdin=PIPE</span></tt>.  Similarly, to get anything other than
<tt class="docutils literal"><span class="pre">None</span></tt> in the result tuple, you need to give <tt class="docutils literal"><span class="pre">stdout=PIPE</span></tt> and/or
<tt class="docutils literal"><span class="pre">stderr=PIPE</span></tt> too.</p>
<p>If the process does not terminate after <em>timeout</em> seconds, a
<a class="reference internal" href="#subprocess.TimeoutExpired" title="subprocess.TimeoutExpired"><tt class="xref py py-exc docutils literal"><span class="pre">TimeoutExpired</span></tt></a> exception will be raised.  Catching this exception and
retrying communication will not lose any output.</p>
<p>The child process is not killed if the timeout expires, so in order to
cleanup properly a well-behaved application should kill the child process and
finish communication:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">proc</span> <span class="o">=</span> <span class="n">subprocess</span><span class="o">.</span><span class="n">Popen</span><span class="p">(</span><span class="o">...</span><span class="p">)</span>
<span class="k">try</span><span class="p">:</span>
    <span class="n">outs</span><span class="p">,</span> <span class="n">errs</span> <span class="o">=</span> <span class="n">proc</span><span class="o">.</span><span class="n">communicate</span><span class="p">(</span><span class="n">timeout</span><span class="o">=</span><span class="mi">15</span><span class="p">)</span>
<span class="k">except</span> <span class="n">TimeoutExpired</span><span class="p">:</span>
    <span class="n">proc</span><span class="o">.</span><span class="n">kill</span><span class="p">()</span>
    <span class="n">outs</span><span class="p">,</span> <span class="n">errs</span> <span class="o">=</span> <span class="n">proc</span><span class="o">.</span><span class="n">communicate</span><span class="p">()</span>
</pre></div>
</div>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">The data read is buffered in memory, so do not use this method if the data
size is large or unlimited.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.3: </span><em>timeout</em> was added.</p>
</div>
</dd></dl>

<dl class="method">
<dt id="subprocess.Popen.send_signal">
<tt class="descclassname">Popen.</tt><tt class="descname">send_signal</tt><big>(</big><em>signal</em><big>)</big><a class="headerlink" href="#subprocess.Popen.send_signal" title="Permalink to this definition">¶</a></dt>
<dd><p>Sends the signal <em>signal</em> to the child.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">On Windows, SIGTERM is an alias for <a class="reference internal" href="#subprocess.Popen.terminate" title="subprocess.Popen.terminate"><tt class="xref py py-meth docutils literal"><span class="pre">terminate()</span></tt></a>. CTRL_C_EVENT and
CTRL_BREAK_EVENT can be sent to processes started with a <em>creationflags</em>
parameter which includes <cite>CREATE_NEW_PROCESS_GROUP</cite>.</p>
</div>
</dd></dl>

<dl class="method">
<dt id="subprocess.Popen.terminate">
<tt class="descclassname">Popen.</tt><tt class="descname">terminate</tt><big>(</big><big>)</big><a class="headerlink" href="#subprocess.Popen.terminate" title="Permalink to this definition">¶</a></dt>
<dd><p>Stop the child. On Posix OSs the method sends SIGTERM to the
child. On Windows the Win32 API function <tt class="xref c c-func docutils literal"><span class="pre">TerminateProcess()</span></tt> is called
to stop the child.</p>
</dd></dl>

<dl class="method">
<dt id="subprocess.Popen.kill">
<tt class="descclassname">Popen.</tt><tt class="descname">kill</tt><big>(</big><big>)</big><a class="headerlink" href="#subprocess.Popen.kill" title="Permalink to this definition">¶</a></dt>
<dd><p>Kills the child. On Posix OSs the function sends SIGKILL to the child.
On Windows <a class="reference internal" href="#subprocess.Popen.kill" title="subprocess.Popen.kill"><tt class="xref py py-meth docutils literal"><span class="pre">kill()</span></tt></a> is an alias for <a class="reference internal" href="#subprocess.Popen.terminate" title="subprocess.Popen.terminate"><tt class="xref py py-meth docutils literal"><span class="pre">terminate()</span></tt></a>.</p>
</dd></dl>

<p>The following attributes are also available:</p>
<dl class="attribute">
<dt id="subprocess.Popen.args">
<tt class="descclassname">Popen.</tt><tt class="descname">args</tt><a class="headerlink" href="#subprocess.Popen.args" title="Permalink to this definition">¶</a></dt>
<dd><p>The <em>args</em> argument as it was passed to <a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> &#8211; a
sequence of program arguments or else a single string.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 3.3.</span></p>
</div>
</dd></dl>

<dl class="attribute">
<dt id="subprocess.Popen.stdin">
<tt class="descclassname">Popen.</tt><tt class="descname">stdin</tt><a class="headerlink" href="#subprocess.Popen.stdin" title="Permalink to this definition">¶</a></dt>
<dd><p>If the <em>stdin</em> argument was <a class="reference internal" href="#subprocess.PIPE" title="subprocess.PIPE"><tt class="xref py py-data docutils literal"><span class="pre">PIPE</span></tt></a>, this attribute is a writeable
stream object as returned by <a class="reference internal" href="functions.html#open" title="open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a>. If the <em>universal_newlines</em>
argument was <tt class="docutils literal"><span class="pre">True</span></tt>, the stream is a text stream, otherwise it is a byte
stream. If the <em>stdin</em> argument was not <a class="reference internal" href="#subprocess.PIPE" title="subprocess.PIPE"><tt class="xref py py-data docutils literal"><span class="pre">PIPE</span></tt></a>, this attribute is
<tt class="docutils literal"><span class="pre">None</span></tt>.</p>
</dd></dl>

<dl class="attribute">
<dt id="subprocess.Popen.stdout">
<tt class="descclassname">Popen.</tt><tt class="descname">stdout</tt><a class="headerlink" href="#subprocess.Popen.stdout" title="Permalink to this definition">¶</a></dt>
<dd><p>If the <em>stdout</em> argument was <a class="reference internal" href="#subprocess.PIPE" title="subprocess.PIPE"><tt class="xref py py-data docutils literal"><span class="pre">PIPE</span></tt></a>, this attribute is a readable
stream object as returned by <a class="reference internal" href="functions.html#open" title="open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a>. Reading from the stream provides
output from the child process. If the <em>universal_newlines</em> argument was
<tt class="docutils literal"><span class="pre">True</span></tt>, the stream is a text stream, otherwise it is a byte stream. If the
<em>stdout</em> argument was not <a class="reference internal" href="#subprocess.PIPE" title="subprocess.PIPE"><tt class="xref py py-data docutils literal"><span class="pre">PIPE</span></tt></a>, this attribute is <tt class="docutils literal"><span class="pre">None</span></tt>.</p>
</dd></dl>

<dl class="attribute">
<dt id="subprocess.Popen.stderr">
<tt class="descclassname">Popen.</tt><tt class="descname">stderr</tt><a class="headerlink" href="#subprocess.Popen.stderr" title="Permalink to this definition">¶</a></dt>
<dd><p>If the <em>stderr</em> argument was <a class="reference internal" href="#subprocess.PIPE" title="subprocess.PIPE"><tt class="xref py py-data docutils literal"><span class="pre">PIPE</span></tt></a>, this attribute is a readable
stream object as returned by <a class="reference internal" href="functions.html#open" title="open"><tt class="xref py py-func docutils literal"><span class="pre">open()</span></tt></a>. Reading from the stream provides
error output from the child process. If the <em>universal_newlines</em> argument was
<tt class="docutils literal"><span class="pre">True</span></tt>, the stream is a text stream, otherwise it is a byte stream. If the
<em>stderr</em> argument was not <a class="reference internal" href="#subprocess.PIPE" title="subprocess.PIPE"><tt class="xref py py-data docutils literal"><span class="pre">PIPE</span></tt></a>, this attribute is <tt class="docutils literal"><span class="pre">None</span></tt>.</p>
</dd></dl>

<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p class="last">Use <a class="reference internal" href="#subprocess.Popen.communicate" title="subprocess.Popen.communicate"><tt class="xref py py-meth docutils literal"><span class="pre">communicate()</span></tt></a> rather than <a class="reference internal" href="#subprocess.Popen.stdin" title="subprocess.Popen.stdin"><tt class="xref py py-attr docutils literal"><span class="pre">.stdin.write</span></tt></a>,
<a class="reference internal" href="#subprocess.Popen.stdout" title="subprocess.Popen.stdout"><tt class="xref py py-attr docutils literal"><span class="pre">.stdout.read</span></tt></a> or <a class="reference internal" href="#subprocess.Popen.stderr" title="subprocess.Popen.stderr"><tt class="xref py py-attr docutils literal"><span class="pre">.stderr.read</span></tt></a> to avoid
deadlocks due to any of the other OS pipe buffers filling up and blocking the
child process.</p>
</div>
<dl class="attribute">
<dt id="subprocess.Popen.pid">
<tt class="descclassname">Popen.</tt><tt class="descname">pid</tt><a class="headerlink" href="#subprocess.Popen.pid" title="Permalink to this definition">¶</a></dt>
<dd><p>The process ID of the child process.</p>
<p>Note that if you set the <em>shell</em> argument to <tt class="docutils literal"><span class="pre">True</span></tt>, this is the process ID
of the spawned shell.</p>
</dd></dl>

<dl class="attribute">
<dt id="subprocess.Popen.returncode">
<tt class="descclassname">Popen.</tt><tt class="descname">returncode</tt><a class="headerlink" href="#subprocess.Popen.returncode" title="Permalink to this definition">¶</a></dt>
<dd><p>The child return code, set by <a class="reference internal" href="#subprocess.Popen.poll" title="subprocess.Popen.poll"><tt class="xref py py-meth docutils literal"><span class="pre">poll()</span></tt></a> and <a class="reference internal" href="#subprocess.Popen.wait" title="subprocess.Popen.wait"><tt class="xref py py-meth docutils literal"><span class="pre">wait()</span></tt></a> (and indirectly
by <a class="reference internal" href="#subprocess.Popen.communicate" title="subprocess.Popen.communicate"><tt class="xref py py-meth docutils literal"><span class="pre">communicate()</span></tt></a>).  A <tt class="docutils literal"><span class="pre">None</span></tt> value indicates that the process
hasn&#8217;t terminated yet.</p>
<p>A negative value <tt class="docutils literal"><span class="pre">-N</span></tt> indicates that the child was terminated by signal
<tt class="docutils literal"><span class="pre">N</span></tt> (POSIX only).</p>
</dd></dl>

</div>
<div class="section" id="windows-popen-helpers">
<h2>17.5.4. Windows Popen Helpers<a class="headerlink" href="#windows-popen-helpers" title="Permalink to this headline">¶</a></h2>
<p>The <a class="reference internal" href="#subprocess.STARTUPINFO" title="subprocess.STARTUPINFO"><tt class="xref py py-class docutils literal"><span class="pre">STARTUPINFO</span></tt></a> class and following constants are only available
on Windows.</p>
<dl class="class">
<dt id="subprocess.STARTUPINFO">
<em class="property">class </em><tt class="descclassname">subprocess.</tt><tt class="descname">STARTUPINFO</tt><a class="headerlink" href="#subprocess.STARTUPINFO" title="Permalink to this definition">¶</a></dt>
<dd><p>Partial support of the Windows
<a class="reference external" href="http://msdn.microsoft.com/en-us/library/ms686331(v=vs.85).aspx">STARTUPINFO</a>
structure is used for <a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> creation.</p>
<dl class="attribute">
<dt id="subprocess.STARTUPINFO.dwFlags">
<tt class="descname">dwFlags</tt><a class="headerlink" href="#subprocess.STARTUPINFO.dwFlags" title="Permalink to this definition">¶</a></dt>
<dd><p>A bit field that determines whether certain <a class="reference internal" href="#subprocess.STARTUPINFO" title="subprocess.STARTUPINFO"><tt class="xref py py-class docutils literal"><span class="pre">STARTUPINFO</span></tt></a>
attributes are used when the process creates a window.</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">si</span> <span class="o">=</span> <span class="n">subprocess</span><span class="o">.</span><span class="n">STARTUPINFO</span><span class="p">()</span>
<span class="n">si</span><span class="o">.</span><span class="n">dwFlags</span> <span class="o">=</span> <span class="n">subprocess</span><span class="o">.</span><span class="n">STARTF_USESTDHANDLES</span> <span class="o">|</span> <span class="n">subprocess</span><span class="o">.</span><span class="n">STARTF_USESHOWWINDOW</span>
</pre></div>
</div>
</dd></dl>

<dl class="attribute">
<dt id="subprocess.STARTUPINFO.hStdInput">
<tt class="descname">hStdInput</tt><a class="headerlink" href="#subprocess.STARTUPINFO.hStdInput" title="Permalink to this definition">¶</a></dt>
<dd><p>If <a class="reference internal" href="#subprocess.STARTUPINFO.dwFlags" title="subprocess.STARTUPINFO.dwFlags"><tt class="xref py py-attr docutils literal"><span class="pre">dwFlags</span></tt></a> specifies <a class="reference internal" href="#subprocess.STARTF_USESTDHANDLES" title="subprocess.STARTF_USESTDHANDLES"><tt class="xref py py-data docutils literal"><span class="pre">STARTF_USESTDHANDLES</span></tt></a>, this attribute
is the standard input handle for the process. If
<a class="reference internal" href="#subprocess.STARTF_USESTDHANDLES" title="subprocess.STARTF_USESTDHANDLES"><tt class="xref py py-data docutils literal"><span class="pre">STARTF_USESTDHANDLES</span></tt></a> is not specified, the default for standard
input is the keyboard buffer.</p>
</dd></dl>

<dl class="attribute">
<dt id="subprocess.STARTUPINFO.hStdOutput">
<tt class="descname">hStdOutput</tt><a class="headerlink" href="#subprocess.STARTUPINFO.hStdOutput" title="Permalink to this definition">¶</a></dt>
<dd><p>If <a class="reference internal" href="#subprocess.STARTUPINFO.dwFlags" title="subprocess.STARTUPINFO.dwFlags"><tt class="xref py py-attr docutils literal"><span class="pre">dwFlags</span></tt></a> specifies <a class="reference internal" href="#subprocess.STARTF_USESTDHANDLES" title="subprocess.STARTF_USESTDHANDLES"><tt class="xref py py-data docutils literal"><span class="pre">STARTF_USESTDHANDLES</span></tt></a>, this attribute
is the standard output handle for the process. Otherwise, this attribute
is ignored and the default for standard output is the console window&#8217;s
buffer.</p>
</dd></dl>

<dl class="attribute">
<dt id="subprocess.STARTUPINFO.hStdError">
<tt class="descname">hStdError</tt><a class="headerlink" href="#subprocess.STARTUPINFO.hStdError" title="Permalink to this definition">¶</a></dt>
<dd><p>If <a class="reference internal" href="#subprocess.STARTUPINFO.dwFlags" title="subprocess.STARTUPINFO.dwFlags"><tt class="xref py py-attr docutils literal"><span class="pre">dwFlags</span></tt></a> specifies <a class="reference internal" href="#subprocess.STARTF_USESTDHANDLES" title="subprocess.STARTF_USESTDHANDLES"><tt class="xref py py-data docutils literal"><span class="pre">STARTF_USESTDHANDLES</span></tt></a>, this attribute
is the standard error handle for the process. Otherwise, this attribute is
ignored and the default for standard error is the console window&#8217;s buffer.</p>
</dd></dl>

<dl class="attribute">
<dt id="subprocess.STARTUPINFO.wShowWindow">
<tt class="descname">wShowWindow</tt><a class="headerlink" href="#subprocess.STARTUPINFO.wShowWindow" title="Permalink to this definition">¶</a></dt>
<dd><p>If <a class="reference internal" href="#subprocess.STARTUPINFO.dwFlags" title="subprocess.STARTUPINFO.dwFlags"><tt class="xref py py-attr docutils literal"><span class="pre">dwFlags</span></tt></a> specifies <a class="reference internal" href="#subprocess.STARTF_USESHOWWINDOW" title="subprocess.STARTF_USESHOWWINDOW"><tt class="xref py py-data docutils literal"><span class="pre">STARTF_USESHOWWINDOW</span></tt></a>, this attribute
can be any of the values that can be specified in the <tt class="docutils literal"><span class="pre">nCmdShow</span></tt>
parameter for the
<a class="reference external" href="http://msdn.microsoft.com/en-us/library/ms633548(v=vs.85).aspx">ShowWindow</a>
function, except for <tt class="docutils literal"><span class="pre">SW_SHOWDEFAULT</span></tt>. Otherwise, this attribute is
ignored.</p>
<p><a class="reference internal" href="#subprocess.SW_HIDE" title="subprocess.SW_HIDE"><tt class="xref py py-data docutils literal"><span class="pre">SW_HIDE</span></tt></a> is provided for this attribute. It is used when
<a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> is called with <tt class="docutils literal"><span class="pre">shell=True</span></tt>.</p>
</dd></dl>

</dd></dl>

<div class="section" id="constants">
<h3>17.5.4.1. Constants<a class="headerlink" href="#constants" title="Permalink to this headline">¶</a></h3>
<p>The <a class="reference internal" href="#module-subprocess" title="subprocess: Subprocess management."><tt class="xref py py-mod docutils literal"><span class="pre">subprocess</span></tt></a> module exposes the following constants.</p>
<dl class="data">
<dt id="subprocess.STD_INPUT_HANDLE">
<tt class="descclassname">subprocess.</tt><tt class="descname">STD_INPUT_HANDLE</tt><a class="headerlink" href="#subprocess.STD_INPUT_HANDLE" title="Permalink to this definition">¶</a></dt>
<dd><p>The standard input device. Initially, this is the console input buffer,
<tt class="docutils literal"><span class="pre">CONIN$</span></tt>.</p>
</dd></dl>

<dl class="data">
<dt id="subprocess.STD_OUTPUT_HANDLE">
<tt class="descclassname">subprocess.</tt><tt class="descname">STD_OUTPUT_HANDLE</tt><a class="headerlink" href="#subprocess.STD_OUTPUT_HANDLE" title="Permalink to this definition">¶</a></dt>
<dd><p>The standard output device. Initially, this is the active console screen
buffer, <tt class="docutils literal"><span class="pre">CONOUT$</span></tt>.</p>
</dd></dl>

<dl class="data">
<dt id="subprocess.STD_ERROR_HANDLE">
<tt class="descclassname">subprocess.</tt><tt class="descname">STD_ERROR_HANDLE</tt><a class="headerlink" href="#subprocess.STD_ERROR_HANDLE" title="Permalink to this definition">¶</a></dt>
<dd><p>The standard error device. Initially, this is the active console screen
buffer, <tt class="docutils literal"><span class="pre">CONOUT$</span></tt>.</p>
</dd></dl>

<dl class="data">
<dt id="subprocess.SW_HIDE">
<tt class="descclassname">subprocess.</tt><tt class="descname">SW_HIDE</tt><a class="headerlink" href="#subprocess.SW_HIDE" title="Permalink to this definition">¶</a></dt>
<dd><p>Hides the window. Another window will be activated.</p>
</dd></dl>

<dl class="data">
<dt id="subprocess.STARTF_USESTDHANDLES">
<tt class="descclassname">subprocess.</tt><tt class="descname">STARTF_USESTDHANDLES</tt><a class="headerlink" href="#subprocess.STARTF_USESTDHANDLES" title="Permalink to this definition">¶</a></dt>
<dd><p>Specifies that the <a class="reference internal" href="#subprocess.STARTUPINFO.hStdInput" title="subprocess.STARTUPINFO.hStdInput"><tt class="xref py py-attr docutils literal"><span class="pre">STARTUPINFO.hStdInput</span></tt></a>,
<a class="reference internal" href="#subprocess.STARTUPINFO.hStdOutput" title="subprocess.STARTUPINFO.hStdOutput"><tt class="xref py py-attr docutils literal"><span class="pre">STARTUPINFO.hStdOutput</span></tt></a>, and <a class="reference internal" href="#subprocess.STARTUPINFO.hStdError" title="subprocess.STARTUPINFO.hStdError"><tt class="xref py py-attr docutils literal"><span class="pre">STARTUPINFO.hStdError</span></tt></a> attributes
contain additional information.</p>
</dd></dl>

<dl class="data">
<dt id="subprocess.STARTF_USESHOWWINDOW">
<tt class="descclassname">subprocess.</tt><tt class="descname">STARTF_USESHOWWINDOW</tt><a class="headerlink" href="#subprocess.STARTF_USESHOWWINDOW" title="Permalink to this definition">¶</a></dt>
<dd><p>Specifies that the <a class="reference internal" href="#subprocess.STARTUPINFO.wShowWindow" title="subprocess.STARTUPINFO.wShowWindow"><tt class="xref py py-attr docutils literal"><span class="pre">STARTUPINFO.wShowWindow</span></tt></a> attribute contains
additional information.</p>
</dd></dl>

<dl class="data">
<dt id="subprocess.CREATE_NEW_CONSOLE">
<tt class="descclassname">subprocess.</tt><tt class="descname">CREATE_NEW_CONSOLE</tt><a class="headerlink" href="#subprocess.CREATE_NEW_CONSOLE" title="Permalink to this definition">¶</a></dt>
<dd><p>The new process has a new console, instead of inheriting its parent&#8217;s
console (the default).</p>
</dd></dl>

<dl class="data">
<dt id="subprocess.CREATE_NEW_PROCESS_GROUP">
<tt class="descclassname">subprocess.</tt><tt class="descname">CREATE_NEW_PROCESS_GROUP</tt><a class="headerlink" href="#subprocess.CREATE_NEW_PROCESS_GROUP" title="Permalink to this definition">¶</a></dt>
<dd><p>A <a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> <tt class="docutils literal"><span class="pre">creationflags</span></tt> parameter to specify that a new process
group will be created. This flag is necessary for using <a class="reference internal" href="os.html#os.kill" title="os.kill"><tt class="xref py py-func docutils literal"><span class="pre">os.kill()</span></tt></a>
on the subprocess.</p>
<p>This flag is ignored if <a class="reference internal" href="#subprocess.CREATE_NEW_CONSOLE" title="subprocess.CREATE_NEW_CONSOLE"><tt class="xref py py-data docutils literal"><span class="pre">CREATE_NEW_CONSOLE</span></tt></a> is specified.</p>
</dd></dl>

</div>
</div>
<div class="section" id="replacing-older-functions-with-the-subprocess-module">
<span id="subprocess-replacements"></span><h2>17.5.5. Replacing Older Functions with the <a class="reference internal" href="#module-subprocess" title="subprocess: Subprocess management."><tt class="xref py py-mod docutils literal"><span class="pre">subprocess</span></tt></a> Module<a class="headerlink" href="#replacing-older-functions-with-the-subprocess-module" title="Permalink to this headline">¶</a></h2>
<p>In this section, &#8220;a becomes b&#8221; means that b can be used as a replacement for a.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p>All &#8220;a&#8221; functions in this section fail (more or less) silently if the
executed program cannot be found; the &#8220;b&#8221; replacements raise <a class="reference internal" href="exceptions.html#OSError" title="OSError"><tt class="xref py py-exc docutils literal"><span class="pre">OSError</span></tt></a>
instead.</p>
<p class="last">In addition, the replacements using <a class="reference internal" href="#subprocess.check_output" title="subprocess.check_output"><tt class="xref py py-func docutils literal"><span class="pre">check_output()</span></tt></a> will fail with a
<a class="reference internal" href="#subprocess.CalledProcessError" title="subprocess.CalledProcessError"><tt class="xref py py-exc docutils literal"><span class="pre">CalledProcessError</span></tt></a> if the requested operation produces a non-zero
return code. The output is still available as the
<a class="reference internal" href="#subprocess.CalledProcessError.output" title="subprocess.CalledProcessError.output"><tt class="xref py py-attr docutils literal"><span class="pre">output</span></tt></a> attribute of the raised exception.</p>
</div>
<p>In the following examples, we assume that the relevant functions have already
been imported from the <a class="reference internal" href="#module-subprocess" title="subprocess: Subprocess management."><tt class="xref py py-mod docutils literal"><span class="pre">subprocess</span></tt></a> module.</p>
<div class="section" id="replacing-bin-sh-shell-backquote">
<h3>17.5.5.1. Replacing /bin/sh shell backquote<a class="headerlink" href="#replacing-bin-sh-shell-backquote" title="Permalink to this headline">¶</a></h3>
<div class="highlight-python3"><div class="highlight"><pre>output=`mycmd myarg`
# becomes
output = check_output([&quot;mycmd&quot;, &quot;myarg&quot;])
</pre></div>
</div>
</div>
<div class="section" id="replacing-shell-pipeline">
<h3>17.5.5.2. Replacing shell pipeline<a class="headerlink" href="#replacing-shell-pipeline" title="Permalink to this headline">¶</a></h3>
<div class="highlight-python3"><div class="highlight"><pre>output=`dmesg | grep hda`
# becomes
p1 = Popen([&quot;dmesg&quot;], stdout=PIPE)
p2 = Popen([&quot;grep&quot;, &quot;hda&quot;], stdin=p1.stdout, stdout=PIPE)
p1.stdout.close()  # Allow p1 to receive a SIGPIPE if p2 exits.
output = p2.communicate()[0]
</pre></div>
</div>
<p>The p1.stdout.close() call after starting the p2 is important in order for p1
to receive a SIGPIPE if p2 exits before p1.</p>
<p>Alternatively, for trusted input, the shell&#8217;s own pipeline support may still
be used directly:</p>
<div class="highlight-python3"><div class="highlight"><pre>output=`dmesg | grep hda`
# becomes
output=check_output(&quot;dmesg | grep hda&quot;, shell=True)
</pre></div>
</div>
</div>
<div class="section" id="replacing-os-system">
<h3>17.5.5.3. Replacing <a class="reference internal" href="os.html#os.system" title="os.system"><tt class="xref py py-func docutils literal"><span class="pre">os.system()</span></tt></a><a class="headerlink" href="#replacing-os-system" title="Permalink to this headline">¶</a></h3>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">sts</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">system</span><span class="p">(</span><span class="s">&quot;mycmd&quot;</span> <span class="o">+</span> <span class="s">&quot; myarg&quot;</span><span class="p">)</span>
<span class="c"># becomes</span>
<span class="n">sts</span> <span class="o">=</span> <span class="n">call</span><span class="p">(</span><span class="s">&quot;mycmd&quot;</span> <span class="o">+</span> <span class="s">&quot; myarg&quot;</span><span class="p">,</span> <span class="n">shell</span><span class="o">=</span><span class="k">True</span><span class="p">)</span>
</pre></div>
</div>
<p>Notes:</p>
<ul class="simple">
<li>Calling the program through the shell is usually not required.</li>
</ul>
<p>A more realistic example would look like this:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="k">try</span><span class="p">:</span>
    <span class="n">retcode</span> <span class="o">=</span> <span class="n">call</span><span class="p">(</span><span class="s">&quot;mycmd&quot;</span> <span class="o">+</span> <span class="s">&quot; myarg&quot;</span><span class="p">,</span> <span class="n">shell</span><span class="o">=</span><span class="k">True</span><span class="p">)</span>
    <span class="k">if</span> <span class="n">retcode</span> <span class="o">&lt;</span> <span class="mi">0</span><span class="p">:</span>
        <span class="nb">print</span><span class="p">(</span><span class="s">&quot;Child was terminated by signal&quot;</span><span class="p">,</span> <span class="o">-</span><span class="n">retcode</span><span class="p">,</span> <span class="n">file</span><span class="o">=</span><span class="n">sys</span><span class="o">.</span><span class="n">stderr</span><span class="p">)</span>
    <span class="k">else</span><span class="p">:</span>
        <span class="nb">print</span><span class="p">(</span><span class="s">&quot;Child returned&quot;</span><span class="p">,</span> <span class="n">retcode</span><span class="p">,</span> <span class="n">file</span><span class="o">=</span><span class="n">sys</span><span class="o">.</span><span class="n">stderr</span><span class="p">)</span>
<span class="k">except</span> <span class="ne">OSError</span> <span class="k">as</span> <span class="n">e</span><span class="p">:</span>
    <span class="nb">print</span><span class="p">(</span><span class="s">&quot;Execution failed:&quot;</span><span class="p">,</span> <span class="n">e</span><span class="p">,</span> <span class="n">file</span><span class="o">=</span><span class="n">sys</span><span class="o">.</span><span class="n">stderr</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="replacing-the-os-spawn-family">
<h3>17.5.5.4. Replacing the <a class="reference internal" href="os.html#os.spawnl" title="os.spawnl"><tt class="xref py py-func docutils literal"><span class="pre">os.spawn</span></tt></a> family<a class="headerlink" href="#replacing-the-os-spawn-family" title="Permalink to this headline">¶</a></h3>
<p>P_NOWAIT example:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">pid</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">spawnlp</span><span class="p">(</span><span class="n">os</span><span class="o">.</span><span class="n">P_NOWAIT</span><span class="p">,</span> <span class="s">&quot;/bin/mycmd&quot;</span><span class="p">,</span> <span class="s">&quot;mycmd&quot;</span><span class="p">,</span> <span class="s">&quot;myarg&quot;</span><span class="p">)</span>
<span class="o">==&gt;</span>
<span class="n">pid</span> <span class="o">=</span> <span class="n">Popen</span><span class="p">([</span><span class="s">&quot;/bin/mycmd&quot;</span><span class="p">,</span> <span class="s">&quot;myarg&quot;</span><span class="p">])</span><span class="o">.</span><span class="n">pid</span>
</pre></div>
</div>
<p>P_WAIT example:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">retcode</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">spawnlp</span><span class="p">(</span><span class="n">os</span><span class="o">.</span><span class="n">P_WAIT</span><span class="p">,</span> <span class="s">&quot;/bin/mycmd&quot;</span><span class="p">,</span> <span class="s">&quot;mycmd&quot;</span><span class="p">,</span> <span class="s">&quot;myarg&quot;</span><span class="p">)</span>
<span class="o">==&gt;</span>
<span class="n">retcode</span> <span class="o">=</span> <span class="n">call</span><span class="p">([</span><span class="s">&quot;/bin/mycmd&quot;</span><span class="p">,</span> <span class="s">&quot;myarg&quot;</span><span class="p">])</span>
</pre></div>
</div>
<p>Vector example:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">os</span><span class="o">.</span><span class="n">spawnvp</span><span class="p">(</span><span class="n">os</span><span class="o">.</span><span class="n">P_NOWAIT</span><span class="p">,</span> <span class="n">path</span><span class="p">,</span> <span class="n">args</span><span class="p">)</span>
<span class="o">==&gt;</span>
<span class="n">Popen</span><span class="p">([</span><span class="n">path</span><span class="p">]</span> <span class="o">+</span> <span class="n">args</span><span class="p">[</span><span class="mi">1</span><span class="p">:])</span>
</pre></div>
</div>
<p>Environment example:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">os</span><span class="o">.</span><span class="n">spawnlpe</span><span class="p">(</span><span class="n">os</span><span class="o">.</span><span class="n">P_NOWAIT</span><span class="p">,</span> <span class="s">&quot;/bin/mycmd&quot;</span><span class="p">,</span> <span class="s">&quot;mycmd&quot;</span><span class="p">,</span> <span class="s">&quot;myarg&quot;</span><span class="p">,</span> <span class="n">env</span><span class="p">)</span>
<span class="o">==&gt;</span>
<span class="n">Popen</span><span class="p">([</span><span class="s">&quot;/bin/mycmd&quot;</span><span class="p">,</span> <span class="s">&quot;myarg&quot;</span><span class="p">],</span> <span class="n">env</span><span class="o">=</span><span class="p">{</span><span class="s">&quot;PATH&quot;</span><span class="p">:</span> <span class="s">&quot;/usr/bin&quot;</span><span class="p">})</span>
</pre></div>
</div>
</div>
<div class="section" id="replacing-os-popen-os-popen2-os-popen3">
<h3>17.5.5.5. Replacing <a class="reference internal" href="os.html#os.popen" title="os.popen"><tt class="xref py py-func docutils literal"><span class="pre">os.popen()</span></tt></a>, <tt class="xref py py-func docutils literal"><span class="pre">os.popen2()</span></tt>, <tt class="xref py py-func docutils literal"><span class="pre">os.popen3()</span></tt><a class="headerlink" href="#replacing-os-popen-os-popen2-os-popen3" title="Permalink to this headline">¶</a></h3>
<div class="highlight-python3"><div class="highlight"><pre><span class="p">(</span><span class="n">child_stdin</span><span class="p">,</span> <span class="n">child_stdout</span><span class="p">)</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">popen2</span><span class="p">(</span><span class="n">cmd</span><span class="p">,</span> <span class="n">mode</span><span class="p">,</span> <span class="n">bufsize</span><span class="p">)</span>
<span class="o">==&gt;</span>
<span class="n">p</span> <span class="o">=</span> <span class="n">Popen</span><span class="p">(</span><span class="n">cmd</span><span class="p">,</span> <span class="n">shell</span><span class="o">=</span><span class="k">True</span><span class="p">,</span> <span class="n">bufsize</span><span class="o">=</span><span class="n">bufsize</span><span class="p">,</span>
          <span class="n">stdin</span><span class="o">=</span><span class="n">PIPE</span><span class="p">,</span> <span class="n">stdout</span><span class="o">=</span><span class="n">PIPE</span><span class="p">,</span> <span class="n">close_fds</span><span class="o">=</span><span class="k">True</span><span class="p">)</span>
<span class="p">(</span><span class="n">child_stdin</span><span class="p">,</span> <span class="n">child_stdout</span><span class="p">)</span> <span class="o">=</span> <span class="p">(</span><span class="n">p</span><span class="o">.</span><span class="n">stdin</span><span class="p">,</span> <span class="n">p</span><span class="o">.</span><span class="n">stdout</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-python3"><div class="highlight"><pre><span class="p">(</span><span class="n">child_stdin</span><span class="p">,</span>
 <span class="n">child_stdout</span><span class="p">,</span>
 <span class="n">child_stderr</span><span class="p">)</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">popen3</span><span class="p">(</span><span class="n">cmd</span><span class="p">,</span> <span class="n">mode</span><span class="p">,</span> <span class="n">bufsize</span><span class="p">)</span>
<span class="o">==&gt;</span>
<span class="n">p</span> <span class="o">=</span> <span class="n">Popen</span><span class="p">(</span><span class="n">cmd</span><span class="p">,</span> <span class="n">shell</span><span class="o">=</span><span class="k">True</span><span class="p">,</span> <span class="n">bufsize</span><span class="o">=</span><span class="n">bufsize</span><span class="p">,</span>
          <span class="n">stdin</span><span class="o">=</span><span class="n">PIPE</span><span class="p">,</span> <span class="n">stdout</span><span class="o">=</span><span class="n">PIPE</span><span class="p">,</span> <span class="n">stderr</span><span class="o">=</span><span class="n">PIPE</span><span class="p">,</span> <span class="n">close_fds</span><span class="o">=</span><span class="k">True</span><span class="p">)</span>
<span class="p">(</span><span class="n">child_stdin</span><span class="p">,</span>
 <span class="n">child_stdout</span><span class="p">,</span>
 <span class="n">child_stderr</span><span class="p">)</span> <span class="o">=</span> <span class="p">(</span><span class="n">p</span><span class="o">.</span><span class="n">stdin</span><span class="p">,</span> <span class="n">p</span><span class="o">.</span><span class="n">stdout</span><span class="p">,</span> <span class="n">p</span><span class="o">.</span><span class="n">stderr</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-python3"><div class="highlight"><pre><span class="p">(</span><span class="n">child_stdin</span><span class="p">,</span> <span class="n">child_stdout_and_stderr</span><span class="p">)</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">popen4</span><span class="p">(</span><span class="n">cmd</span><span class="p">,</span> <span class="n">mode</span><span class="p">,</span> <span class="n">bufsize</span><span class="p">)</span>
<span class="o">==&gt;</span>
<span class="n">p</span> <span class="o">=</span> <span class="n">Popen</span><span class="p">(</span><span class="n">cmd</span><span class="p">,</span> <span class="n">shell</span><span class="o">=</span><span class="k">True</span><span class="p">,</span> <span class="n">bufsize</span><span class="o">=</span><span class="n">bufsize</span><span class="p">,</span>
          <span class="n">stdin</span><span class="o">=</span><span class="n">PIPE</span><span class="p">,</span> <span class="n">stdout</span><span class="o">=</span><span class="n">PIPE</span><span class="p">,</span> <span class="n">stderr</span><span class="o">=</span><span class="n">STDOUT</span><span class="p">,</span> <span class="n">close_fds</span><span class="o">=</span><span class="k">True</span><span class="p">)</span>
<span class="p">(</span><span class="n">child_stdin</span><span class="p">,</span> <span class="n">child_stdout_and_stderr</span><span class="p">)</span> <span class="o">=</span> <span class="p">(</span><span class="n">p</span><span class="o">.</span><span class="n">stdin</span><span class="p">,</span> <span class="n">p</span><span class="o">.</span><span class="n">stdout</span><span class="p">)</span>
</pre></div>
</div>
<p>Return code handling translates as follows:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="n">pipe</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">popen</span><span class="p">(</span><span class="n">cmd</span><span class="p">,</span> <span class="s">&#39;w&#39;</span><span class="p">)</span>
<span class="o">...</span>
<span class="n">rc</span> <span class="o">=</span> <span class="n">pipe</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="k">if</span> <span class="n">rc</span> <span class="ow">is</span> <span class="ow">not</span> <span class="k">None</span> <span class="ow">and</span> <span class="n">rc</span> <span class="o">&gt;&gt;</span> <span class="mi">8</span><span class="p">:</span>
    <span class="nb">print</span><span class="p">(</span><span class="s">&quot;There were some errors&quot;</span><span class="p">)</span>
<span class="o">==&gt;</span>
<span class="n">process</span> <span class="o">=</span> <span class="n">Popen</span><span class="p">(</span><span class="n">cmd</span><span class="p">,</span> <span class="n">stdin</span><span class="o">=</span><span class="n">PIPE</span><span class="p">)</span>
<span class="o">...</span>
<span class="n">process</span><span class="o">.</span><span class="n">stdin</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="k">if</span> <span class="n">process</span><span class="o">.</span><span class="n">wait</span><span class="p">()</span> <span class="o">!=</span> <span class="mi">0</span><span class="p">:</span>
    <span class="nb">print</span><span class="p">(</span><span class="s">&quot;There were some errors&quot;</span><span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="replacing-functions-from-the-popen2-module">
<h3>17.5.5.6. Replacing functions from the <tt class="xref py py-mod docutils literal"><span class="pre">popen2</span></tt> module<a class="headerlink" href="#replacing-functions-from-the-popen2-module" title="Permalink to this headline">¶</a></h3>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">If the cmd argument to popen2 functions is a string, the command is executed
through /bin/sh.  If it is a list, the command is directly executed.</p>
</div>
<div class="highlight-python3"><div class="highlight"><pre><span class="p">(</span><span class="n">child_stdout</span><span class="p">,</span> <span class="n">child_stdin</span><span class="p">)</span> <span class="o">=</span> <span class="n">popen2</span><span class="o">.</span><span class="n">popen2</span><span class="p">(</span><span class="s">&quot;somestring&quot;</span><span class="p">,</span> <span class="n">bufsize</span><span class="p">,</span> <span class="n">mode</span><span class="p">)</span>
<span class="o">==&gt;</span>
<span class="n">p</span> <span class="o">=</span> <span class="n">Popen</span><span class="p">(</span><span class="s">&quot;somestring&quot;</span><span class="p">,</span> <span class="n">shell</span><span class="o">=</span><span class="k">True</span><span class="p">,</span> <span class="n">bufsize</span><span class="o">=</span><span class="n">bufsize</span><span class="p">,</span>
          <span class="n">stdin</span><span class="o">=</span><span class="n">PIPE</span><span class="p">,</span> <span class="n">stdout</span><span class="o">=</span><span class="n">PIPE</span><span class="p">,</span> <span class="n">close_fds</span><span class="o">=</span><span class="k">True</span><span class="p">)</span>
<span class="p">(</span><span class="n">child_stdout</span><span class="p">,</span> <span class="n">child_stdin</span><span class="p">)</span> <span class="o">=</span> <span class="p">(</span><span class="n">p</span><span class="o">.</span><span class="n">stdout</span><span class="p">,</span> <span class="n">p</span><span class="o">.</span><span class="n">stdin</span><span class="p">)</span>
</pre></div>
</div>
<div class="highlight-python3"><div class="highlight"><pre><span class="p">(</span><span class="n">child_stdout</span><span class="p">,</span> <span class="n">child_stdin</span><span class="p">)</span> <span class="o">=</span> <span class="n">popen2</span><span class="o">.</span><span class="n">popen2</span><span class="p">([</span><span class="s">&quot;mycmd&quot;</span><span class="p">,</span> <span class="s">&quot;myarg&quot;</span><span class="p">],</span> <span class="n">bufsize</span><span class="p">,</span> <span class="n">mode</span><span class="p">)</span>
<span class="o">==&gt;</span>
<span class="n">p</span> <span class="o">=</span> <span class="n">Popen</span><span class="p">([</span><span class="s">&quot;mycmd&quot;</span><span class="p">,</span> <span class="s">&quot;myarg&quot;</span><span class="p">],</span> <span class="n">bufsize</span><span class="o">=</span><span class="n">bufsize</span><span class="p">,</span>
          <span class="n">stdin</span><span class="o">=</span><span class="n">PIPE</span><span class="p">,</span> <span class="n">stdout</span><span class="o">=</span><span class="n">PIPE</span><span class="p">,</span> <span class="n">close_fds</span><span class="o">=</span><span class="k">True</span><span class="p">)</span>
<span class="p">(</span><span class="n">child_stdout</span><span class="p">,</span> <span class="n">child_stdin</span><span class="p">)</span> <span class="o">=</span> <span class="p">(</span><span class="n">p</span><span class="o">.</span><span class="n">stdout</span><span class="p">,</span> <span class="n">p</span><span class="o">.</span><span class="n">stdin</span><span class="p">)</span>
</pre></div>
</div>
<p><tt class="xref py py-class docutils literal"><span class="pre">popen2.Popen3</span></tt> and <tt class="xref py py-class docutils literal"><span class="pre">popen2.Popen4</span></tt> basically work as
<a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">subprocess.Popen</span></tt></a>, except that:</p>
<ul class="simple">
<li><a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> raises an exception if the execution fails.</li>
<li>the <em>capturestderr</em> argument is replaced with the <em>stderr</em> argument.</li>
<li><tt class="docutils literal"><span class="pre">stdin=PIPE</span></tt> and <tt class="docutils literal"><span class="pre">stdout=PIPE</span></tt> must be specified.</li>
<li>popen2 closes all file descriptors by default, but you have to specify
<tt class="docutils literal"><span class="pre">close_fds=True</span></tt> with <a class="reference internal" href="#subprocess.Popen" title="subprocess.Popen"><tt class="xref py py-class docutils literal"><span class="pre">Popen</span></tt></a> to guarantee this behavior on
all platforms or past Python versions.</li>
</ul>
</div>
</div>
<div class="section" id="legacy-shell-invocation-functions">
<h2>17.5.6. Legacy Shell Invocation Functions<a class="headerlink" href="#legacy-shell-invocation-functions" title="Permalink to this headline">¶</a></h2>
<p>This module also provides the following legacy functions from the 2.x
<tt class="docutils literal"><span class="pre">commands</span></tt> module. These operations implicitly invoke the system shell and
none of the guarantees described above regarding security and exception
handling consistency are valid for these functions.</p>
<dl class="function">
<dt id="subprocess.getstatusoutput">
<tt class="descclassname">subprocess.</tt><tt class="descname">getstatusoutput</tt><big>(</big><em>cmd</em><big>)</big><a class="headerlink" href="#subprocess.getstatusoutput" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <tt class="docutils literal"><span class="pre">(status,</span> <span class="pre">output)</span></tt> of executing <em>cmd</em> in a shell.</p>
<p>Execute the string <em>cmd</em> in a shell with <tt class="xref py py-meth docutils literal"><span class="pre">Popen.check_output()</span></tt> and
return a 2-tuple <tt class="docutils literal"><span class="pre">(status,</span> <span class="pre">output)</span></tt>. Universal newlines mode is used;
see the notes on <a class="reference internal" href="#frequently-used-arguments"><em>Frequently Used Arguments</em></a> for more details.</p>
<p>A trailing newline is stripped from the output.
The exit status for the command can be interpreted
according to the rules for the C function <tt class="xref c c-func docutils literal"><span class="pre">wait()</span></tt>.  Example:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">subprocess</span><span class="o">.</span><span class="n">getstatusoutput</span><span class="p">(</span><span class="s">&#39;ls /bin/ls&#39;</span><span class="p">)</span>
<span class="go">(0, &#39;/bin/ls&#39;)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">subprocess</span><span class="o">.</span><span class="n">getstatusoutput</span><span class="p">(</span><span class="s">&#39;cat /bin/junk&#39;</span><span class="p">)</span>
<span class="go">(256, &#39;cat: /bin/junk: No such file or directory&#39;)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">subprocess</span><span class="o">.</span><span class="n">getstatusoutput</span><span class="p">(</span><span class="s">&#39;/bin/junk&#39;</span><span class="p">)</span>
<span class="go">(256, &#39;sh: /bin/junk: not found&#39;)</span>
</pre></div>
</div>
<p>Availability: POSIX &amp; Windows</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.3.4: </span>Windows support added</p>
</div>
</dd></dl>

<dl class="function">
<dt id="subprocess.getoutput">
<tt class="descclassname">subprocess.</tt><tt class="descname">getoutput</tt><big>(</big><em>cmd</em><big>)</big><a class="headerlink" href="#subprocess.getoutput" title="Permalink to this definition">¶</a></dt>
<dd><p>Return output (stdout and stderr) of executing <em>cmd</em> in a shell.</p>
<p>Like <a class="reference internal" href="#subprocess.getstatusoutput" title="subprocess.getstatusoutput"><tt class="xref py py-func docutils literal"><span class="pre">getstatusoutput()</span></tt></a>, except the exit status is ignored and the return
value is a string containing the command&#8217;s output.  Example:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="gp">&gt;&gt;&gt; </span><span class="n">subprocess</span><span class="o">.</span><span class="n">getoutput</span><span class="p">(</span><span class="s">&#39;ls /bin/ls&#39;</span><span class="p">)</span>
<span class="go">&#39;/bin/ls&#39;</span>
</pre></div>
</div>
<p>Availability: POSIX &amp; Windows</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 3.3.4: </span>Windows support added</p>
</div>
</dd></dl>

</div>
<div class="section" id="notes">
<h2>17.5.7. Notes<a class="headerlink" href="#notes" title="Permalink to this headline">¶</a></h2>
<div class="section" id="converting-an-argument-sequence-to-a-string-on-windows">
<span id="converting-argument-sequence"></span><h3>17.5.7.1. Converting an argument sequence to a string on Windows<a class="headerlink" href="#converting-an-argument-sequence-to-a-string-on-windows" title="Permalink to this headline">¶</a></h3>
<p>On Windows, an <em>args</em> sequence is converted to a string that can be parsed
using the following rules (which correspond to the rules used by the MS C
runtime):</p>
<ol class="arabic simple">
<li>Arguments are delimited by white space, which is either a
space or a tab.</li>
<li>A string surrounded by double quotation marks is
interpreted as a single argument, regardless of white space
contained within.  A quoted string can be embedded in an
argument.</li>
<li>A double quotation mark preceded by a backslash is
interpreted as a literal double quotation mark.</li>
<li>Backslashes are interpreted literally, unless they
immediately precede a double quotation mark.</li>
<li>If backslashes immediately precede a double quotation mark,
every pair of backslashes is interpreted as a literal
backslash.  If the number of backslashes is odd, the last
backslash escapes the next double quotation mark as
described in rule 3.</li>
</ol>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<dl class="last docutils">
<dt><a class="reference internal" href="shlex.html#module-shlex" title="shlex: Simple lexical analysis for Unix shell-like languages."><tt class="xref py py-mod docutils literal"><span class="pre">shlex</span></tt></a></dt>
<dd>Module which provides function to parse and escape command lines.</dd>
</dl>
</div>
</div>
</div>
</div>


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      <div class="sphinxsidebar">
        <div class="sphinxsidebarwrapper">
  <h3><a href="../contents.html">Table Of Contents</a></h3>
  <ul>
<li><a class="reference internal" href="#">17.5. <tt class="docutils literal"><span class="pre">subprocess</span></tt> &#8212; Subprocess management</a><ul>
<li><a class="reference internal" href="#using-the-subprocess-module">17.5.1. Using the <tt class="docutils literal"><span class="pre">subprocess</span></tt> Module</a><ul>
<li><a class="reference internal" href="#frequently-used-arguments">17.5.1.1. Frequently Used Arguments</a></li>
<li><a class="reference internal" href="#popen-constructor">17.5.1.2. Popen Constructor</a></li>
<li><a class="reference internal" href="#exceptions">17.5.1.3. Exceptions</a></li>
</ul>
</li>
<li><a class="reference internal" href="#security-considerations">17.5.2. Security Considerations</a></li>
<li><a class="reference internal" href="#popen-objects">17.5.3. Popen Objects</a></li>
<li><a class="reference internal" href="#windows-popen-helpers">17.5.4. Windows Popen Helpers</a><ul>
<li><a class="reference internal" href="#constants">17.5.4.1. Constants</a></li>
</ul>
</li>
<li><a class="reference internal" href="#replacing-older-functions-with-the-subprocess-module">17.5.5. Replacing Older Functions with the <tt class="docutils literal"><span class="pre">subprocess</span></tt> Module</a><ul>
<li><a class="reference internal" href="#replacing-bin-sh-shell-backquote">17.5.5.1. Replacing /bin/sh shell backquote</a></li>
<li><a class="reference internal" href="#replacing-shell-pipeline">17.5.5.2. Replacing shell pipeline</a></li>
<li><a class="reference internal" href="#replacing-os-system">17.5.5.3. Replacing <tt class="docutils literal"><span class="pre">os.system()</span></tt></a></li>
<li><a class="reference internal" href="#replacing-the-os-spawn-family">17.5.5.4. Replacing the <tt class="docutils literal"><span class="pre">os.spawn</span></tt> family</a></li>
<li><a class="reference internal" href="#replacing-os-popen-os-popen2-os-popen3">17.5.5.5. Replacing <tt class="docutils literal"><span class="pre">os.popen()</span></tt>, <tt class="docutils literal"><span class="pre">os.popen2()</span></tt>, <tt class="docutils literal"><span class="pre">os.popen3()</span></tt></a></li>
<li><a class="reference internal" href="#replacing-functions-from-the-popen2-module">17.5.5.6. Replacing functions from the <tt class="docutils literal"><span class="pre">popen2</span></tt> module</a></li>
</ul>
</li>
<li><a class="reference internal" href="#legacy-shell-invocation-functions">17.5.6. Legacy Shell Invocation Functions</a></li>
<li><a class="reference internal" href="#notes">17.5.7. Notes</a><ul>
<li><a class="reference internal" href="#converting-an-argument-sequence-to-a-string-on-windows">17.5.7.1. Converting an argument sequence to a string on Windows</a></li>
</ul>
</li>
</ul>
</li>
</ul>

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  <p class="topless"><a href="concurrent.futures.html"
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  <h4>Next topic</h4>
  <p class="topless"><a href="sched.html"
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